Memoirs of the Horticultural Society of New York (1927)
Papers Presented at the International Conference on Flower and Fruit Sterility August 12-14, 1926
Research Department of The Conard-Pyle Company

Sterility in roses is very frequent, although the pollen of most sterile seed-bearers is potent on other varieties, only two cases of sterility of both sexes having come to my knowledge, one being a double form of yellow Rosa xanthina and the other, Agnes, a hybrid of R. Rugosa and Persian Yellow of recent introduction. Several species are nearly sterile with their own pollen and entirely so with foreign pollen, while their pollen is potent on other varieties; such as Rosa bella, Rosa alpina and its hybrids, Rosa lutea and Rosa centifolia. Almost every moss-rose is sterile, the only exceptions I know being Blanche Moreau, Mme. Louis Leveque and Henri Martin, but the latter has so little moss to bequeath that nearly every one of its hybrids and even selfings are without moss. Blanche Moreau seedlings have, so far been worthless and Mme. Louis Leveque reverts, no matter what pollen has been used, to the centifolia type, losing its moss altogether. In the days of the moss-rose popularity, a certain number of named varieties were introduced, but these were either bud mutations or merely pollen hybrids having only a suspicion of moss. Often their only claim to the name of moss was a glandular calyx emitting the peculiar scent of the true moss-rose.

Major Hurst of Cambridge University made a special study of the moss-rose and its sterility or fecundity. The moss-rose originated from bud mutations of the R. centifolia and all these bud mutations of first generation were sterile, but those of second generation (bud mutation from bud mutation) showed a certain fertility, but these were only lightly mossed. Quoting Hurst, "No records of the production of fertile seeds by either the typical R. centifolia or R. muscosa can be traced in botanical or horticultural literature. No fully formed and mature fruits have been observed on either form at Burbage (his old family estate) under normal conditions, during the last 70 years, though partly formed fruits containing no seeds have been frequently found." However, this sterility or rather infertility of the moss-rose is not always due to the involuted multiplication of the petals of the flower peculiar to both the typical R. centifolia and R. muscosa whose tightly balled petals and petaloid stamens seem to inhibit the natural development of pistils. The only fruits I ever obtained from Blanche Moreau and Mme. Louis Leveque were through artificial operation, when at an early age the petals, petaloid stamens, and stamens were carefully removed, and the pistils released and allowed to develop freely. Even at that the results were only one fruit to twenty failures, and the seedlings proved either worthless or identical to the mother. I tried again this summer on the mossiest of all the moss-roses, an old variety known as English Pink Moss. At first, about half the operated blooms showed signs of impregnation, grew to a certain size and presently dried up. I understand that several hybridists lately have taken up again the moss-rose, but with what success I know not.

I mentioned Agnes as a patent example of sterility in R. rugosa hybrids. A close study of its organs showed misformed pistils and ovaries, the potency of its pollen, although pointing to sterility, is still undefined because of its paucity of stamens, which as in the moss-rose are covered and smothered by petals and petaloid stamens. I was occasionally able to free some of the anthers which seemed to release pollen, but which, however, brought no result, although applied to proved seed bearing varieties.

When the R. rugosa species became known, it was heralded as the forebearer of a new race of garden roses, and men like Gravereaux and Cochet took it up with enthusiasm, but the hybrids thus produced proved almost all sterile as to seed bearing, some at the first generation; others at the second, thus precluding the perpetuation, through a long descendance, of the commending features of the rugosa species, and to retain these dominant features in their entirety, or nearly so, the results so far obtained seem to indicate that the R. rugosa should be used as seed bearer; in the hybrids produced from rugosa pollen, the rugosa characters are so subdued as to be sometimes hardly recognized. Microscopical examination of the pollen of these three species (centifolia, muscosa and rugosa) is reported by Major Hurst as follows: "In centifolia and muscosa, 95 per cent of the grains were malformed, the chief difference being the presence in R. muscosa of a number of abnormally large grains showing signs of hypertrophy, and in both forms, degeneration of pollen was found in the early tetrad age. This result contrasts remarkably with the 99 per cent of well-formed grains found in R. rugosa and R. arvensis in all stages of development, but resembles rather the large percentage of malformed grains found in R. Wichuraiana and R. laxa."

The malformation of R. Wichuraiana pollen grains is probably the reason why, while we have so many Wichuraiana hybrids, I do not know of any issued from Wichuraiana pollen. From my own experience the pollen of Wichuraiana hybrids has invariably been sterile, yet the Wichuraiana type self-seeds very readily, practically every bloom being fertilized and the percentage of germination of these seeds is high.

A great many rose species hybrids are sterile after the first generation, and it was a great handicap to Dr. Van Fleet in his species hybridizing not to be able to carry on further generations.

Among the horticultural varieties of roses, many hybrids are sterile. The Bourbon strain at one time offered great promise, but the sterility of the hybrids discouraged the breeders and that strain has practically been abandoned. Souvenir de la Malmaison, one of those sterile Bourbons, gave me once a well developed selfing with three seeds, two of which germinated, only one surviving, the general character being Bourbon, but with enough changes in both foliage and bloom to surmise foreign pollen, although it might have been a case of parthenogenesis. Since then I have again and again tried artificial pollination, but without success.

A case of near sterility worth noticing is American Pillar. It produces a profusion of fruits which in the fall and winter are very ornamental, but many hips are seedless; in the others, one or two seeds only, mostly empty, and a casual one only out of a large quantity of seeds will have a live germ.

The garden roses of today are so highly hybridized, many representing a succession of selected selfings, that a large percentage have run their course of fertility. Some are sterile with one pollen of proved potency and fertile with another. Although the pigmentation of two prospective parents may not have direct influence on fertility, yet I have observed that the more extreme the combinations the less successful I was in obtaining fertility. As an example Hawlmark Crimson, a blackish crimson, is sterile both ways when crossed with a deep yellow, and also is R. Moyesii.

Have the soil and original method of propagation a direct relation to the fertility or sterility of a plant? We have long noted here that grafted plants of R. Hugonis, for example, will profusely bear seeds, while plants grown from cuttings are very scant seed bearers, almost approaching sterility. Paul's Scarlet Climber as an own root plant may be considered as sterile, but a grafted plant will bear both self- and hand-pollinated seeds. I have also noted that plants of the same variety in different parts of the nursery have a different seed bearing capacity, although both receive the same amount of sunshine. As an instance, R. bracteata and R. Altaica at one location are practically sterile, while a short distance away, but in a different soil, nearly every bloom, either hand- or self-pollinated, sets fruit.

Climatic conditions may also have something to do: a rose hybridizer of experience in Canada writes that Mme. Caroline Testout and Gruss an Teplitz are totally sterile for him, yet they notoriously are prolific seed bearers in other sections and in Europe.

How long does rose pollen retain its vitality? I do not know whether this question has ever been answered. I have obtained fertility by pollen preserved from two to three months in absorbent manila envelopes. P. Nabonnand of France told me that he used pollen a year old, and Pernet Ducher was successful with three-year-old pollen, both claiming that pollen to retain its potency must be in a container that will absorb moisture, and warned against using glass tubes.

Darwin, 'Double flowers-their origin', Gardeners' Chronicle, no. 36, 9 September 1843, p. 628.

"It is well known that plants (and indeed animals, as I could show by a series of facts) when placed out of their natural conditions, become, often from apparently slight and unintelligible causes, sterile. How many American plants fail in producing pollen in this country! the anthers of the Persian and Chinese Lilacs, as I observed this summer, are as destitute of good pollen as if they had been hybrids. Other plants produce good pollen, but are defective, as it appears, in their ovules, as their germen never swells. Linnaeus has remarked that most Alpine plants, when cultivated in the lowlands, are rendered quite sterile. In most of these cases, we see that sterility is compatable with long life and health."