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Both cases are more common on individuals with broad stripes than on plants bearing only the narrower red lines, as might be expected, but even on the almost purely yellow individuals they may be seen from time to time. Bud-variations produce branches with spikes of uniform red flowers. Every bud of the plant seems to have equal chances to be transformed in this way.
Such cases should likewise be discarded, since they bring in confusing elements. If we review the long list of recorded cases by these strict methods of criticism very few instances will be found that satisfy legitimate demands. On this ground it is by far safer in the present state of our knowledge, to accept bud-variations only as direct proofs of true atavism.
As far as my experiments go, they are the rule, and parent-plants that do not give such reversions, at least in some of their offspring, are very rare, if not wholly wanting. Bud-variations and variations within the spike I have as yet only observed on the striped individuals, and never on the red ones, though I am confident that they might appear in larger series of experiments.
Bud-variations, such as the appearance of a moss-rose on a common rose, or of a nectarine on a peach-tree, offer good instances of spontaneous variations; but even in these cases, if we bear in mind the power of a minute drop of poison in producing complex galls, we ought not to feel too sure that the above variations are not the effect of some local change in the nature of the sap, due to some change in the conditions.
But before taking it up it is as well to learn the real signification of recessiveness in the hybrids themselves. Recessive characters are shown by those rare cases, in which hybrids revert to the varietal parent in the vegetative way. In other words by bud-variations or sports, analogous to the splitting of Adam's laburnum into its parents, by means of bud-variation already described.
The striped flowers repeated their character in 98% of their offspring, the red twigs in only 71%, the remaining individuals sporting into the opposite group. In the following year I continued the experiment with the seeds of the offspring of the red bud-variations. The striped individuals gave 95%, but in the red ones only 84% of the progeny remained true to the parent type.
On the other hand there is a larger group of cases of reversion by buds, which is probably not of hybrid nature, nor due to innate inconstancy of the variety, but must be considered as pure atavism. I refer to the bud-variations of so many of our cultivated varieties of shrubs and trees. Many of them are cultivated because of their foliage.
Perhaps it might even throw some light on the intimate nature of the bud-variations of ever-sporting varieties in general. Sectional variations remain to be tested as to the degree of inheritance exhibited, and the different occurrences as to the breadth of the streaks require similar treatment.
And even these may not always be relied on, as some hybrids are liable to split up in a vegetative way, and in doing so to give rise to bud-variations that are in many respects apparently similar to cases of atavism. But fortunately such instances are as yet very rare.
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