Proc. Am. Soc. Hort. Sci. 37: 983-992 (1939)
Crossing Relations of Some Diploid Species of Roses
By J. C. RATSEK, S. H. YARNELL, and W. S. FLORY, JR.,
Texas Agricultural Experiment Station, A. and M. College, College Station, Tex.

THE Welch strain of Rosa multiflora Thunb. is widely used by commercial growers Texas as an understock. Because it has certain disadvantages a rather extensive breeding program to secure improved rootstocks was inaugurated by the Texas Agricultural Experiment Station at its Substation No. 2, which is in the commercial rose area in Smith county. The garden roses represent in many cases rather complicated admixtures of wild forms, and it was felt that a series of interspecific crosses would be more likely to yield promising rootstock material than crosses within a single species.

The genus Rosa has long been of interest to taxonomists and cytogeneticists because of the large amount of variability encountered in nature and the ensuing difficulties of classification. Many of the species have been examined cytologically by various workers and as a result chromosome numbers are pretty well established. For tabulations of chromosome counts see Gaiser (4-7), and Tischler (13). Blackburn (1), Erlanson (2), Hurst (8), and Tackholm (11, 12) report extensive observations on chromosome numbers in Rosa. Since the number of crosses either made or attempted has become rather large it is proposed to confine this paper to a discussion of crossing relationships between species that are reported to be diploid (2n = 14), Data on the degree of fertility or sterility found may be of some use to breeders and may contribute to our knowledge of genetic relationships among the different species. A cytological study now under way will be reported later. Promising seedlings will be included in a rootstock test as they become sufficiently mature.

MATERIAL AND METHODS

The parent species used in the crosses were obtained from the following sources: Bobbink and Atkins, the Arnold Arboretum, Cornell University, and the United States Department of Agriculture. Two or three forms of Rosa multiflora were obtained locally. The three hybrids used were sent to us by Professor T. J. Maney of Iowa State College. The species were checked with descriptions in Willmott's "The Genus Rosa" (14), and in Rehder's "Manual of Trees and Shrubs" (9). We have followed Rehder's arrangement of species with respect to sections of the genus.

It is of interest, from the standpoint of the inter-relationship between cytogenetics and taxonomy, that most of the known diploid species have been found among the sections Synstyliae and Cinnamomeae. Rehder recognized 15 sections of Rosa. Of the 20 diploid species used in these crosses eight belong to the Synstyliae, nine to the Cinnamomeae, two to the Pimpinellifoliae, and one to the Caroliniae, no other section being represented.

Pollen was collected from flowers about to open by teasing the anthers out with a comb, allowing them to dehisce on a piece of paper, and transferring the pollen to a vial. Buds nearly ready to open were emasculated by pinching off the perianth, either with the finger nails or with forceps, and removing stray stamens. During the first three seasons the emasculated flowers were covered with a small brown paper sack and pollinated a day or two later. The last year the flowers were pollinated immediately after emasculation and then bagged. The latter method seems to have been entirely satisfactory where flowers of the proper stage of development were chosen.

The first year seeds were sown directly in the cold frame in the fall without stratification. There was serious damage by ants and neither need nor germination records were obtained. The second year a comparison was made of agar and peat moss as media for germinating seeds. Both groups were held at a temperature of 40 to 45 degrees F. Subsequently the use of peat moss was abandoned in favor of the agar culture. As the seedlings germinated they were transferred to flats in the greenhouse and later potted or placed in nursery rows. Germination took place from 6 to 18 months after planting. Seeds not germinated by this time were sown in the open ground, but no further germination has been observed.

RESULTS AND DISCUSSION

Data on the proportion of successful crosses and resulting seed production are presented. Attention is called to the heading of the first and last columns of each table. Successful crosses are listed numerically for each year, thus 67-38 means cross No. 67 made in 1938. Unsuccessful crosses are designated by the year in parentheses (-38). The "per cent filled" is based on the average number of seeds found ill from 10 to 20 hips resulting from open pollination, as 100 per cent. These figures are for the 1939 season only. The amount of seasonal variation is not yet known. These percentages, therefore, are strictly valid only for the 1939 crosses. Percentages are figured to the nearest whole number.

While only a beginning has been made on a study of the seedlings the evidence leads us to conclude that the crosses between diploids yielded true hybrids.

With the exception of sterilities that can be assigned to definite genetic factors, the relative ease with which a cross can be made is generally taken as an indication of the degree of genetic similarity of the forms involved. The same may be said for our results with diploid roses. For example in the section Synstyliae, per cent set among varieties of the same species averaged 29.6, while among distinct species it was 18.0. Among species of the Cinnamomeae, 44.7 per cent of tile pollinations were successful, while between species of the Cinnamomeae and the Synstyliae the average set was 15.6 per cent, and the reciprocal was 7.0 per cent. Certain exceptions were observed. Rosa multiflora Cathayensis yielded no fruits from 49 pollinations with the R. multiflora varieties Chenault, Upright, and Welch (Table I). At the other extreme R. blanda. Ait, a species of the Cinnamomeae, was highly fertile with R. Hugonis Hemsl., belonging to the Pimpinellifoliae (Table V).

Some species set much more readily in inter-specific crosses than others. Rosa blanda can be cited again as a conspicuous example of a species relatively fertile in many crosses. It averaged 62.3 per cent set in crosses with seven other species of the Cinnamomiae. The hips were filled 91 per cent as well as those open pollinated. Similar results with R. blanda have been discussed by Maney in conversation with the senior author. In contrast to this R. setigera Michx. of the Synstyliae averaged only 1 per cent set with six species of this section.

An explanation of these exceptions can only be speculative. Cathayensis is the only one of the Rosa multiflora varieties that has given these results. It was originally described as a distinct species by Rehder and Wilson (10) and the results may reflect a greater genetic difference for this variety. The ease of crossing R. blanda may be due to one or more fertility factors effective with other species. These might influence the rate of pollen tube growth or perhaps the compatibility of genic complements during development of the embryo.

A comparison of results secured with species considered to be synonymous can be made in a few cases. Rosa abyssinica R. Br. x abyssinica gave 40 per cent set, while this species x R. moschata Mill. with which it is synonymous failed (Table I). Rosa Fendleri Crep. Is considered by Erlanson (3) to be a synonym of R. Woodsii Lindl. Rosa blanda x Fendleri set 39 per cent, while blanda x Woodsii set 78 per cent, but the first cross averaged a few more seeds per hip. Corresponding figures for the reciprocal crosses are 87 and 79. Rosa Fendleri can also be compared with R. Woodsii in crosses with the Welch strain of R. multiflora. Percentages of set were 32 and 53 with average seeds per hip of 10.4 and 11 .6 respectively. Since age of flower varied somewhat in all of the crosses, number of seeds per hip is probably a better criterion than per cent set, although complete failure of all pollinations cannot be accounted for on this basis. Results with these species rated as synonymous are considered to be comparable to those secured with varieties of the same species.

Fewer seeds were set in controlled crosses, in most cases, than with open pollination. There are seven exceptions, three of them involving Rosa blanda and four R. soulieana. The pollinators of R. blanda were R. pisocarpa and R. rugosa; those for R. soulieana were R. abyssinica, R. multiflora Cathayensis, and R. Wichuraiana. In considering the results it might be well to recall that the parental material has not as yet been examined by us cytologically, although chromosome counts have been made on a number of the seedlings. The classification of these species as diploid follows the information now available, although R. blanda and R. pisocarpa have also been reported with higher chromosome numbers.

No seeds were obtained with the hybrid (Rosa multiflora x blanda) used as pollen parent on five species. Pollen from R. multiflora x rugosa produced seed on R. blanda but not on R. setigera, a poor seed parent, or on R. Wichuraiana. 

The results have been examined from the standpoint of Hurst's grouping of diploid species (8). He considers similar species to be geographical subspecies of a single empirical species. He designates five such groups to include all diploid species and refers to the haploid set of seven chromosomes of each group by letter: A, B, C, D and E.

Pure species are AA, BB, CC, DD or EE and inter-group hybrids are AB, CD, BE and so on. Our crosses are grouped on this basis in Table VI.

TABLE I.—IMMEDIATE RESULTS OF CROSSES BETWEEN SPECIES OF ROSA OF THE SECTION SYNSTYLIAE

Cross
No.
Seed Parent Pollen Parent No
Flowers
Crossed
Per Cent
Set
Seeds per Hip Per Cent*
Filled
Cross Open
Pollinated
67-38 R. abyssinica R. Br. (A)** R. abyssinica (A) 10 40 5.7 30.5 19
(-38) R. abyssinica R. Br. (A)** R. moschata nivea (A) 10 0 — — —
(-38) R. abyssinica R. Br. (A)** R. multiflora Upright (A) 10 0 — — —
16-37 R. arvensis Huds. (A) R. multiflora Cathay. (A) 23 4 3.0 5.6 54
70-38 R. Helenae R. & W. (A) R. abyssinica (A) 8 25 1.0 10.4 10
(-37) R. Helenae R. & W. (A) R. multiflora Cath. (A) 21 0 — — —
(-38) R. Helenae R. & W. (A) R. multiflora Upright (A) 9 0 — — —
75-39 R. Helenae R. & W. (A) R. multiflora Upright (A) 15 60 3.2 10.4 31
35-39 R. moschata Mill alba (A) R. moschata grandifl. (A) 15 80 2.2 3.5 63
36-39 R. moschata Mill alba (A) R. moschata nivea 19 21 2.7 3.5 79
73-39 R. moschata Mill flor. R. moschata grandifl. 27 7 1.0 14.5 7
71-39 R, moschata Mill flor. R. moschata nivea 28 .32 3.0 14.5 21
72-39 R. moschata Mill flor. R. multiflora Upright (A) 26 96 5.7 14.5 39
(-37) R. moschata Mill nivea R. multiflora Clien. Wel. (A) 50 0 — — —
60-38 R. multiflora Thunb. (A) R. multiflora Chenault (A) 48 21 2.5 10.3 24
62-38 R. multiflora Thunb. (A) R. multiflora Welch 137 45 9.3 10.3 90
(-38) R. multiflora Cathay. (A) R. moschata florib. (A) 11 0 — — —
53-39 R. multiflora Cathay. (A) R. moschata grandif. 28 4 2.0 10.5 19
(-38) R. multiflora Cathay. (A) R, multiflora Chen. Up. Wel. (A) 49 0 — — —
65-38 R. multiflora Chenault R. multiflora, Welch (A) 35 80 5.5 9.3 59
61-39 R. multiflora Upright R. moschata grandif. (A) 23 3.5 2.9 10.4 28
(-36) R. multiflora Welch R. moschata (A) 10 0 — — —
(-38) R. setigera Michx. (A) R. abyssinica (A) 20 0 — — —
(-38) R. setigera Michx. (A) R. arvensis (A) 20 0 — — —
(-38, -39) R. setigera Michx. (A) R. moschata alba, flor.          
    R. grandiflora, nivea (A) 86 0 — — —
(-37,-38,-39) R. setigera Michx. (A) R. multiflora Cath., Chen., platy. Up. (A) 119 0 — — —
108-39 R. setigera Michx. (A) R. multiflora Cath. (A) 14 7 1.0 4.9 20
(-38) R. setigera Michx. (A) R. soulieana Crep. (A) 20 0 — — —
87-37 R. soulieana Crep. (A) R. arvensis (A) 18 39 1.9 7.0 27
(-37,-38) R. soulieana Crep. (A) R. moschata alba, flor, grandiflora (A) 68 0 — — —
90-38 R. soulieana Crep. (A) R. moschata nivea 21 10 1.5 7.0 21
(-38) R. soulieana Crep. (A) R. multiflora, plat, (A) 38 0 — — —
(-36) R. soulieana Crep. (A) R. multiflora Cathay. (A) 7 7 — — —
81-37 R. soulieana Crep. (A) R. multiflora Cathay. (A) 47 72 12.4 7.0 178
82-38 R. soulieana Crep. (A) R. multiflora Chenault 21 5 1.0 7.0 14
(-37, -39) R. soulieana Crep. (A) R. multiflora Chenault 71 0   — —
84-37 R. soulieana Crep. (A) R. multiflora. Iowa† 45 51 1.7 7.0 23
84-38 R. soulieana Crep. (A) R. multiflora Upright 19 5 1.0 7.0 14
(-39) R. soulieana Crep. (A) R. multiflora Upright 21 0 — — —
83-38 R. soulieana Crep. (A) R. multiflora Welch 24 25 1.5 7.0 21
82-37 R. soulieana Crep. (A) R. Wichuraiana (A) 34 32 11.0 7.0 157
108-38 R. Wichuraiana Crep. (A) R. abyssinica (A) 20 30 2.3 23.8 10
112-38 R. Wichuraiana Crep. (A) R. arvensis (A) 22 14 1.3 23.8 5
(-39) R. Wichuraiana Crep. (A) R. moschata grand. (A) 22 0 — — —
116-38 R. Wichuraiana Crep. (A) R. moschata nivea 20 15 3.0 23.8 13
96-39 R. Wichuraiana Crep. (A) R. rnoschata nivea 22 10 1.0 23.8 4
(-39) R. Wichuraiana Crep. (A) R. multiflora Up., plat. (A) 42 0 — — —
98-39 R. Wichuraiana Crep. (A) R. multiflora Cath. 22 9 1.0 23.8 4
99-39 R. Wichuraiana Crep. (A) R. multiflora Chen. 22 9 1.0 23.8 4
(-38) R. Wichuraiana Crep. (A) R. multiflora Chen. 50 0 — — —
101-38 R. Wichuraiana Crep. (A) R. muitflora Upright 18 44 4.1 23.8 17
(-39) R. Wichuraiana Crep. (A) R. multiflora Upright 21 0 — — —
100-38 R. Wichuraiana Crep. (A) R. multiflora Welch 16 31 2.0 23.8 8
109-38 R. Wichuraiana Crep. (A) R. soulieana (A) 16 19 1.7 23.8 7
*Per cent of open pollinated.
**Refers to Hurst's classification.
†This may not be pure multiflora.

TABLE II—IMMEDIATE RESULTS OF CROSSES BETWEEN SPECIES OF ROSA THE SECTION CINNAMOMEAE

Cross
Number
Seed Parent Pollen Parent Number
Flowers
Crossed
Per Cent
Set
Number
Seed per Hip
Per Cent*
filled
Cross Open
Pollinated
(-39) R. Beggeriana Schr. R. blanda (D) 12 0 — — —
(-39) R. Beggeriana Schr. R. Fendleri (D) 12 0 — — —
7-38 R. blanda Ait. (D)† R. Fendleri (D) 18 39 21.8 22.0 99
9-38 R. blanda Ait. (D)† R. giraldi (E) 36 56 20.5 22.0 93
49-37 R. blanda Ait.(D)† R. pisocarpa Gray (D) 21 28 22.6 22.0 103
15-38 R. blanda Ait. (D)† R. pisocarpa Gray (D) 21 86 16.4 22.0 75
16-38 R. blanda Ait. (D)† R. rugosa Thunb. (C) 23 91 25.3 22.0 115
19-38 R. blanda Ait. (D)† R. Willmottiae Hemsl. (B) 24 58 14.0 22.0 64
47-37 R. blanda Ait. (D)† R. Woodsii (D) 18 78 19.1 22.0 87
11-37 R. Fendleri Crep. (D) R. blanda (D) 23 87 18.2 23.3 78
(-37) R. Giraldii Crep. (E) R. blanda (D) 47 0 — — —
(-37) R. Giraldii Crep. (E) R. rugosa alba (C) 26 0 — — —
3-38 R. rugosa alba (C) R. blanda (D) 11 9 44.0 63.6 69
45-37 R. Woodsii Lindl. (D) R. blanda (D) 34 79 18.2 — —
4-37 R. Woodsii Lindl. (D) R. rugosa alba (C) 15 60 13.3 — —
*Per Cent of open pollinated.
†Refers to Hurst’s classification.

It is possible to compare ease of crossing, within and between groups in two cases. Inter-specific crosses among the AA species resulted in 18 per cent set and approximately 40 per cent fill (compared to open pollination). Per cent set of AA species in crosses with BB, CC and DD species as pollen parents ranged from 6.7 to 9.1 with per cent fill about half that of intra-group inter-specific crosses. In the case of the DD group both per cent set and fill were high. Both were higher in the type cross D x C than in D x D but a little lower in the D x A and D x B than either D x D or D x C. These inter-group results are not due to the high fertility of Rosa blanda alone but are supported by results from R. Woodsii as seed parent.

Of the species used in our crosses the AA group coincides with the section Synstyliae. In the Cinnamomeae are included BB, CC, DD and EE groups. Rosa Willmottiae (BB) was not used as seed parent. R. rugosa (CC) gave 9 per cent set with R. blanda. R. Fendleri. R. blanda and R. Woodsii (DD) exhibited a high degree of fertility. R. Giraldii (EE) set nothing with R. blanda (47 pollinations) and nothing with R. rugosa (26 pollinations). These results seem to be more consistent with Hurst's classification than with the grouping based on the section Cinnamomeae. Additional evidence on this point can be found in Table IV. In spite of this fact the available evidence is against placing all forms in one of Hurst's letter groups within a single species as he has done, For example, inter-varietal crosses of the AA group set around 30 per cent with about 45 per cent as good achene set as open pollinated flowers. The corresponding figures for interspecific crosses among species with AA genoms are 18 and 39 (Table VI). The number of combinations is reasonably large in each case.

TABLE III—IMMED1ATE RESULTS OF CROSSES BETWEEN SPECIES OF ROSA OF THE SECTIONS SYNSTYLIAE AND CINNAMOMEAE

Cross
No.
Seed Parent Pollen Parent No.
Flowers
Crossed
Per Cent
Set
Seeds per Hip Per
Cent*
Filled
Crossed Open
Pollinated
(-37) Rosa Helenae (A)† R. Beggeriana 14 0 — — —
76-39 R. Helenae (A)† R. blanda (D) 16 37 3.0 10.4 29
(-39) R. Helenae (A)† R. Fendleri (D) 12 0 — — —
72-38 R. Helenae (A)† R. rugosa (C) 9 11 2.0 10.4 19
(-39) R. Helenae (A)† R. rugosa (C) 12 0 — — —
(-39) R. moschata alba (A) R. blanda (D) 4 0 — — —
(-39) R. moschata florib. R. blanda (D) 33 0 — — —
c-37) R. moschata grand. R. Woodsii (D) 28 0 — — —
(-37) R. moschata nivea R. rugosa (C) 47 0 — — —
(-39) R. multiflora Cathay. (A) R. blanda (D) 27 0 — — —
(-36, -39) R. multiflora Cath. R. Fendleri (D) 28 0 — — —
(-39) R. multiflora Cathay. R. Giraldii (E) 24 0 — — —
(-36) R. multiflora Welch R. gymnocarpa Nutt. (B) 4 0 — — —
(-39) R. multiflora Cathay. R. rugosa alba (C) 28 0 — — —
(-39) R. multiflora Cathay. R. Willmottiae (B) 27 0 — — —
(-36) R. multiflora Welch R. Woodsii (D) 3 0 — — —
(-38, -39) R. setigera (A) R. blanda (D) 45 0 — — —
107-39 R. setigera (A) R. blanda (D) 12 17 3.0 4.9 61
(-38, -39) R. setigera (A) R. fendleri (D) 35 0 — — —
(-38,-39) R. setigera (A) R. Giraldii (E) 35 0 — — —
(-39) R. setigera (A) R. pisocarpa (D) 12 0 — — —
(-38, -39) R. setigera (A) R. rugosa (C) 104 0 — — —
(-38, -39) R. setigera (A) R. Willmottiae (B) 34 0 — — —
88-38 R. Soulieana (A) R. blanda (D) 26 11 1.3 7.0 19
(-39) R. Soulieana (A) R. blanda (D) 20 0 — — —
96-38 R. Soulieana (A) R. Fendleri (D) 24 s 1.0 7.0 14
89-37 R. Soulieana (A) R. Giraldii (E) 51 2 1.0 7.0 14
80-38 R. Soulieana (A) R. Giraldii (E) 19 5 1.0 7.0 14
92-38 R. Soulieana (A) R. pisocarpa (D) 17 24 1.0 7.0 14
90-37 R .Soulieana (A) R. rugosa (C) 33 15 1.6 7.0 23
76-38 R, Soulieana (A) R. rugosa (C) 20 5 1.0 7.0 14
75-37 R. Soulieana (A) R. rugosa alba 58 74 9.0 7.0 129
91-38 R. Soulieana (A) R. Willmottiae (B) 22 5 1.0 7.0 14
117-37 R. Wichuraiana (A) R. blanda (D) 19 5 3.0 23.8 13
86-39 R. Wïchuraiana (A) R. blanda (D) Is 6 1.0 23.8 4
1.14-38 R. Wichuraiana (A) R. fendleri (D) 19 16 2.3 23.8 10
(-39) R. Wichuraiana (A) R. fendleri (D) 16 0 — — —
(-39) R. Wichuraiana (A) R. Giraldii (E) 20 0 — — —
102-39 R. Wichuraiana (A) R. pisocarpa (D) 24 50 7.8 23.8 33
103-38 R. Wichuraiana (A) R. rugosa (C) 20 15 1.0 23.8 4
(-39) R. Wichuraiana (A) R. rugosa (C) 22 0 — — —
(-39) R. Wichuraiana (A) R. rugosa alba 19 0 — — —
(-38, -39 R. Wichuraiana (A) R. Willmottiae (B) 35 0 — — —
 *Per cent of open pollinated.
†Refers to Hurst's classification.

TABLE IV—IMMEDIATE RESULTS OF CROSSES BETWEEN SPECIES OF ROSA OF THE SECTIONS CINNAMOMEAE AND SYNSTYLIAE

Cross
No.
Seed Parent Pollen Parent No.
Flowers
Crossed
Per Cent
Set
Seeds per Hip Per Cent*
Filled
Crossed Open Pollinated
(-39) Rosa Beggeriana R. moschata grandif. (A)† 15 0 — — —
(-39) R. Beggeriana R. multiflora Cath., Chen., Upright 37 0 — — —
5-38 R. blanda (D)† R. multiflora Chenault (A) 31 42 12.1 22.0 55
7-37 R. blanda (D)† R. multiflora platy. 43 2 5.0 22.0 23
51-37 R. blanda (D)† R. multiflora Welch 38 32 16.4 22.0 75
9-37 R. Fendleri (D) R. multiflora Iowa (A)** 30 17 10.4 23.3 45
42-37 R. Fendleri (D) R. multiflora Welch 31 32 10.4 23.3 45
(-36,-37) R. Giraldii (E) R. multiflora Cath., Wel. 80 0 — — —
(-36) R. gymnocarpa (B) R. multiflora Cathay. (A) 1.5 7 — — —
(-37,-39) R. rugosa (C) R. multiflora Upright (A) 13 0 — — —
(-36) R. Woodsii (D) R. multiflora Cathay (A) 27 .33 — — —
46-37 R. Woodsii (D) R. multiflora Welch 32 53 11.6 — —
 *Per cent of open pollinated.
**This may not be pure multiflora.
†Refers to Hurst's classification.

TABLE V—IMMEDIATE RESULTS OF ADDITIONAL CROSSES BETWEEN SPECIES AND CERTAIN HYBRIDS OF ROSA INVOLVING SEVERAL SECTIONS OF ONE GENUS

Cross No. Seed Parent Pollen Parent No.
Flowers
Crossed
Per
Cent
Set
Seeds per Hip Per
Cent*
Filled
Crossed Open Pollinated
Synstyliae x (Synstyliae x Cinnamomeae)
(-39) Rasa setigera (A)† R. multiflora (A) x rugosa (C) 12 0 — — —
(-39) R. setigera (A)f R. multiflora (A) x blanda (D) 17 0 — — —
(-39) R. Soulieana (A) R. multiflora (A) x blanda (D) 21 0 — — —
(-39) R. Wichuraiana (A) R. multiflora (A) x blanda (D) 20 0 — — —
(-39) R. Wichuraiana (A) R. multiflora (A) x rugosa (C) 17 0 — — —
Cinnamomeae x (Synstyliae x Cinnamomeae)
(-39) R. Beggeriana R. multiflora (A) x blanda (D) 11 0 — — —
3-39 R. blanda (D) R. multiflora (A) x rugosa (C) 17 71 14.2 22.0 65
(-39) R. rugosa (C) R. multiflora (A) x blanda (D) 12 0 — — —
Synstyliae x Pimpinellifoliae
77-39 R. Helenae (A) R. xanthina allard (B) 13 15 1.0 10.4 10
74-39 R. moschata florib. (A) R. xanthina allard (B) 27 7 1.0 14.5 7
(-37) R. moschata grand. R. Hugonis (B) 36 0 — — —
52-39 R. multiflora Cathay. (A) R. xanthina allard (B) 31 3 2.0 10.5 19
58-39 R. multiflora Upright R. xanthina allard 23 13 1.7 10.4 16
(-38) R. setigera (A) R. Hugonis (B) 20 0 — — —
120-38 R. setigera (A) R. xanthina allard (B) 20 10 2.0 4.9 41
(-39) R. setigera (A) R. xanthina allard (B) 15   — — —
(-37) R. Soulieana (A)  R. Hugonis (B) 33 0 0 — — —
81-38 R. Soulieana (A) R. Hugonis (B) 23 22 1.2 7.0 17
88-37 R. Soulieana (A) R. xanthina (B) 42 7 — — —
(-38) R. Soulieana (A) R. xanthina (B) 22 0 2.0 7.0 29
85-38 R. Soulieana (A) R. xanthina allard 24 37 3.0 7.0 43
(-39) R. Soulieana (A) R. xanthina allard 21 0 — — —
115-38 R. Wichuraiana (A) R. Hugonis (B) 19 26 2.2 23.8 9
106-39 R. Wichuraiana (A) R. xanthina (B) 19 10 1.5 23.8 6
102-38 R. Wichuraiana (A) R. xanthina allard 21 38 1.7 23.8 7
(-39) R. Wichuraiana (A) R. xanthina allard 20 0 — — —
Cinnamomeae  x Pimpinellifolia
(-39) R. Beggeriana R xanthina allard (B) 14 0 — — —
10-38 R. blanda (D) R. Hugonis (B) 21 67 27.2 22.0 124
4-38 R. blanda (D) R .xanthina allard (B) 22 14 5.0 22.0 23
1-39 R. blanda (D) R. xanfhina allard (B) 12 9 1.0 22.0 5
28-37 R. Woodsii (D) R. xanthina (13) 15 53 9.2   41
Caroliniae x Cinnamomeae
(-37) R. nitida Willd. (C) R. rugosa (C) 21 0 — — —
*Per cent of open pollinated.
†Refers to Hursts classification.

TABLE VI—COMPATIBILITY OF SPECIES ARRANGED ACCORDING TO HURST’S SYSTEM

Type Cross Average
Per Cent Set.
 Number
Combinations
Average
Per Cent Fill
Number
Combinations
A x A* 29.6 11 45.2 8
A x A† 18.0 20 39.1 16
B x B — — — —
C x C 0.0 1 — —
D x D 62.2 5 88.1 4
A x B 0.7 15 20.3 7
B x A 3.5 2 — —
A x C 6.8 U 26.0 3
C x A 0.0 1 — —
A x D 0.1 10 23,5 8
D x A 30.7 3 48.0 2
B x C — — — —
C x B — — — —
B x D — — — —
D x B 47.2 4 00.8 4
C x D 9.0   69.0 1
D x C 75.5 2 115.0 1
*Different varieties of the same species.
†Different species.

LITERATURE CITED

  1. BLACKBURN, K, Chromosomes and classification in the genus Rosa. Amer. Nat. 59:200-205. 1925.
  2. ERLANSON, E. W. Cytological conditions and evidences for hybridity in North American wild roses. Ann. Bot. 35:159-188. 1921.
  3. Experimental data for a revision of the North American wild roses. Bot. Gaz. 96:197-259. 1934.
  4. GAISER, L. O. A list of chromosome numbers in angiosperms. Genetica 8:401-484. 1926.
  5. — Chromosome numbers in angiosperms. II. Biblio. Genetica 6:171-466. 1930.
  6. — Chromosome numbers in angiosperms. III. Genetica 12: 159-256. 1930.
  7. — Chromosome numbers in angiosperms. IV. Biblio. Genetica 10:105-250. 1933.
  8. HURST, C. C. Differential polyploidy in the genus Rosa L. Verh. V. Inern. Kongr. Vererb. Berlin 2: 866-906. 1928.
  9. REHDER, A. Manual of Cultivated Trees and Shrubs. pp. 427-450. Macmillan, New York. 1934.
  10. — and WILSON, E. H. In Sargent, Plantae Wilsonianae II 304, 310. 1915.
  11. TACKHOLM, G. On the cytology of the genus Rosa. Svensk Bot. Tids. 14: 301-311. 1920.
  12. — Zytologische studien über die gattung Rosa. Acta Hort. Bergiani 7:97-381. 1922.
  13. TISCHLER, G. Pflanzliche chromosomenzahlen. Tab. Biol. 7:109-226. 1931. 11:281-304. 1935. 12:57-115. 1936.
  14. WILLMOTT, ELLEN. The Genus Rosa. 2 Vols. John Murray, London. 1914.