The Gardeners’ Chronicle ser. 3, 9: 618-621 (May 16, 1891)
"Greenhouse" Rhododendrons

IT is a matter of regret that the history of the origin of many of our florists' productions has not been recorded. Being cultivated for commercial purposes, it is rarely that any record has been kept of the successive parentages of the hybrids and crosses raised. It would have been not only interesting to know the complete genealogy of e.g., our Pelargoniums, but many points in the physiology of cross-breeding might have been studied, if the effects had been critically examined at every stage.

In the case of Orchid crosses, the necessity for systematic examination and record has already become urgent, owing to the great number of crossed and hybridised plants already produced, and the vast number which are waiting their turn. These artificial crosses and hybrids often give the clue to many so-called "natural hybrids," whose origin and parentage are doubtful. Moreover, the physiological and morphological questions involved are of very great interest, quite apart from questions of commercial importance and decorative value.

* A list of hybrids and crosses between North American species and Old World Rhododendrons was published by Mr. STANDISH in Beck's Florist, 1851, p. 170; and in The Florist, 1856, p. 246.

With a view of gaining information on some of these points, Mr. HENSLOW has made a study of what are now known as the "Greenhouse Rhododendrons," mostly raised by Messrs. VEITCH. Messrs. VEITCH & SONS supplied Mr. HENSLOW with the flowers and foliage of the hybrids and crosses which they had raised between seven species of East Indian Rhododendron.* He gave some account of his investigations at the meeting of the Royal Horticultural Society on Tuesday last,

† These are:—
1, R. jasminiflorum (white), from Malacca;
2, R. Lobbii (crimson) Borneo;
3, R. Brookeanum var. gracile (straw-coloured), Borneo;
4, R. javanicum (orange), Java;
5, R. Teysmanni (golden-yellow), Sumatra;
6, R. malayanum (cerise), Sumatra;
7, R. multicolor (lemon), and var. Curtisii (crimson), Sumatra.
CybeRose note: In the Bot. Mag. t. 6850, the author wrote that the R. javanicum pictured in t. 4336, "is, I think, unmistakably the R. Teysmanni, Miquel".

Mr. HENSLOW'S object was to endeavour to trace the effect of each parent in the offspring, and, if possible, to deduce some practical results. He first described the seven species,† calling attention to the various forms and colours of the flowers, and the different shapes of the leaves.

First Generations or True Hybrids.— These seven species are, it appears, perfectly fertile together; and four generations have been raised up to the present time, by crossing the descendants, and re-crossing them with the original species in various ways. About 180 have now flowered. These have formed two well-marked sections, one being larger, and the other smaller-flowered. The latter group is due to the introduction of the species R. multicolor (lemon-coloured), and its variety R. multicolor var. Curtisii (crimson), which gives the name multicolor to the section. A third section is called balsaminiflorum, from the resemblance to double Balsams, as the members of this group are all semi- or quite double.

The first true hybrid was raised by Mr. JAMES VEITCH,  in 1850, between R. jasminiflorum (white) and R. javanicum (orange). The combination gave a totally new type of form. The long tube of the corolla of the female, and the broad limb of that of the male parent, were combined, and resulted in a new and elegant type of flower. It was named Princess Royal (pink). This result in colour illustrates a fact which occurred again later, as well as with other flowers, as, Abutilon and Begonia; namely, that when orange is crossed with white, one of the two colours, included in the former, is gradually eliminated. It is usually the yellow; pinks of various shades remaining. Sometimes, but seemingly less frequently, it is the reverse, the yellow being left; as in the cross called Minerva, between Princess Alexandra (white) and R. javanicum (orange); nine other sister-crosses being rose-coloured, of various tints.

The next hybrid of importance was obtained by crossing R. Lobbii (crimson) with R. Brookeanum, var. gracile (straw-coloured). The combination of yellow with crimson produced brilliant scarlets; while the long and curved tube of R. Lobbii was much improved, the border being greatly enlarged, and the curvature of the tube straightened.

R. multicolor (lemon), and its variety Curtisii (crimson), were used in crossing R. jasminiforum (white), R. javanicum (orange), and R. Teysmanni (golden yellow), as well as several crosses, with the result that this small-flowering species greatly reduced the size of the others with which it was united, at the same time imparting its own form. These crosses have formed the "Multicolor section." They might be called the "pompons of the entire group.

Second generations.— Of these the first raised was Princess Alexandra (white). This was obtained by re-crossing Princess Royal (pink) with R. jasminiflorum (white). The result was that the white now eliminated the pink; the form of the corolla of Princess Royal being retained. These two were the sources of numerous others of subsequent generations. Thus, besides Princess Alexandra, six other results were obtained by crossing Princess Royal. Of the most important are the offspring of Princess Royal (pink) with R. Brookeanum, see  fig. 123, p. 621 (yellow). They are called Princess Frederica, Crown Princess of Germany, and Duchess of Teck. In these the yellow has prevailed, scarcely any trace of pink being discernible, except in the anthers; though it has just prevented the yellow from being true. These three laid the foundation of a fresh series of the third generation.

Mr. HENSLOW next proceeded to give some account of the different effects produced, as follows:—

1. Elimination of Colour.— It has been already observed that while crossing orange with white, it generally gave rise to pink but sometimes to yellow; yet it is not infrequent for pink when crossed with orange, to produce a nearly similar effect, in so far as the colours of the parents may be greatly reduced if not quite eliminated. This was the case when Princess Royal (pink) was crossed with R. javanicum (orange), as well as by R. Teysmanni (golden yellow). The result was the very palest primrose colour. The same effect was produced when R. Teysmanni was crossed by R. Taylori (pink) as the pollen-bearing parent. The offspring is called " Purity," a plant of the fourth generation. This, therefore, affords a second practical hint, for two series of very delicate shades of pink and cream, varying to Primrose-yellow, were raised. In both cases, by combining the pink and yellow in the parents.

2. Restoration of Colour. — Another interesting effect is the restoration of colour. It has already been seen that Princess Alexandra (white) was obtained by recrossing Princess Royal (pink) with the original species, R. jasminiflorum (white). But when Princess Alexandra was crossed with the pure yellow-coloured R. Brookeanum, not merely was the yellow totally eliminated, but the pink from the grandparent, Princess Royal, was more or less completely restored in the offsprings called Taylori and Maiden's Blush.

3. Prepotency.— The fact was not unknown in the experience of raisers of crosses in other plants, that the flowers of the offspring may be identical with those of one or other of the parents, and show no intermediate characters. As illustrations of this fact, the following cases may be mentioned:— Maiden's Blush, of a pinky-cream colour, when crossed by the golden-yellow R. Teysmanni, bore one scarcely distinguishable from the latter. Again, when the large-flowered orange-coloured Monarch was crossed by the very small-flowered and cerise-coloured R. malayanum, the offspring were practically identical with the latter. Similarly, R. multicolor var. Curtisii (crimson), is prepotent over nearly every form with which it is crossed; so that, whether it be a true species, a hybrid, or subsequent cross of any generation, the result is almost identically the same in each case.

4. Dissociation of Colours.— There are no instances of spots or streaks occurring; but there is occasionally a marked difference in colour between the border or limb and the throat of the tube. The crosses between R. multicolor var. Curtisii and R. Teysmanni illustrate this feature.

5. Effects of Multifold Crossing.— Mr. VEITCH has raised several crosses of the fourth generation, combining four or five species in the results. The following is a selection to illustrate the fact that the species first used frequently retain no visible trace of their existence in the latest offspring, which is much more conformable to the colour of the species last introduced. Hippolyta is the offspring of Queen of the Yellows and R. multicolor, var. Curtisii. It contains R. jasminifiorum, R. javanicum (twice), R. Brookeanum, and R. multicolor, var. Curtisii. The form resembles that of R. multicolor, only larger; the increased size being originally due to R. javanicum. The leaf is an enlarged form of R. multicolor. Little Beauty and No. 29 are the offspring of Monarch and R. malayanum. They contain five species, and one of them twice, viz., R, jasminiflorum, R. javanicum (twice), R. Lobbii, R. Brookeanum, and R. malayanum. Yet the result is almost purely R. malayanum, the leaf only being large, and even that has russet-brown scales similar to this species.

6. Balsaminiflorum Section.— The origin of this was as follows: — A single stamen in one flower only, on a single truss of a member of the second generation (probably Princess Frederica or sister cross) was slightly petaloid. The pistil of that flower was fertilised by pollen taken from the other anthers of the same flower, being thus "self-fertilised." Fifteen seeds were obtained, all of which proved to be semi- or quite double. Dissociation took place in colour and form, revealing the ancestry, as types illustrating Princess Royal, Princess Alexandra, R. javanicum, &c., appeared, the colours being white, pink, yellow, and orange.

A practical result is here obviously disclosed, for this interesting experiment reveals how "doubles" may be fixed (but not created) by self-fertilisation. Just as it is well-known that the rule applies to other peculiarities which it may be thought desirable to retain. Self-fertilisation being comparable to multiplication by buds, such as "cuttings," &c,

Summary of the General Effect of Colours on Crossing.— It is frequently asserted that the male parent prevails over the reproductive system, thereby imparting the characteristics of the corolla, &c, while the female transmits any specialties in the foliage. Though this is sometimes true, as e.g., in the "bigener" raised by Mr. Veitch between the Rhododendron Lord Wolseley" and Azalea indica "Stella"; it was the reverse with Princess Royal, and it would be more correct to say that the offspring may resemble either parent in either way and in various degrees, according to unexplainable prepotencies within them, respectively.

1. The Combination of Colours: Red and yellow may combine, and produce colours ranging from a bright yellow-orange to scarlet-crimson.— 2. The Reduction of Colours: White and crimson may produce pink. Pink and crimson may produce shades of pink or rose. Light yellow and golden-yellow may produce primrose-yellow.— 3. The Separation and Partial Elimination of one of the Colours: White and orange may produce pink or yellow. Pink and orange may produce yellow.— 4. The Elimination of all, or nearly all, Colour: White, orange, or yellow, crossed with pink, may produce white.— 5. The Dissociation of Colours: A crimson or yellow crossed with orange may produce reddish lobes and a yellow tube, or vice versa.— 6. The prepotency of Colours: Crimson or yellow may completely overpower yellow and orange, one or other alone being transmitted.— 7. The Restoration of Colours: Reds and yellows can be restored without a fresh infusion, if the tint be "in the blood" from some previous generation, whether in the corolla or anthers and filaments only.

Effects of Form in Crossing.— Starting with R. jasminiflorum and R. Lobbii, which have long tubes and small borders, and R. javanicum, R. Brookeanum, and R. Teysmanni, with short tubes and broad borders, a large number of the forms raised have corollas intermediate in so far that they have long tubes and enlarged bordera. This is the characteristic feature of many of the larger forms. An additional result is obtained with R. Lobbii, which has a long but curved tube and small border, when crossed with other large-flowered species. In this case the curvature soon disappears. When the small-flowered R. multicolor is used in combination with the large-flowered species, the effect is to reduce the size, so that by means of this species a smaller-flowered race has been obtained, called the "Multicolor section," analogous to the pompons among Dahlias and Chrysanthemums. Besides the fact that the size of a flower may be greatly reduced by crossing it with a small-flowered species, the effect is sometimes to produce a corolla larger than that of either parent. An example is found in No. 158, which is the offspring of Pr. Frederica and R. javanicum. In this case not only are the lobes greatly enlarged, but, as far as experience goes, permanently increased in number from five to six, or even seven.

Another practical result may be here mentioned, that, as a rule, better forms and colours are secured by recrossing crosses by a true species rather than by a form which is itself a cross. Though it is not an absolute rule, some exquisite results being obtained by combinations of crosses, as e.g., in several of the offspring of Princess Alexandra (second generation) with Duchess of Edinburgh (true hybrid).

Effects of the Leaf in Crossing.— It is by no means the rule, as far as these Rhododendrons are concerned, that the female parent affects the foliage, while the male influences the flowers of the offspring, as has been often asserted. Thus, the first hybrid raised negatives this idea; Princess Royal possesses the foliage of the male parent R. javanicum, the elliptical leaf the other, R. jasminiflorum being completely ignored, this being very blunt at both ends, while it is tapering in the others.