230 THE ORCHID REVIEW. [AuGuSsT, 1915. 
protoplasms of diverse origin by a non-sexual process. This identity is not 
always admitted, and we have seen attempts to produce the graft hybrid 
known as Cytisus Adami by sexual means, though without success. The 
inference is that the obstacle is a mechanical, not a physiological one, and 
such obstacles are not unfamiliar to hybridists. Several other graft hybrids 
are known, and it would be interesting to attempt to reproduce them by 
the sexual method, for mechanical obstacles may not always exist. Their 
constancy from seed might also be tested, for we believe that some of them 
are fertile. The experiment has failed with Cytisus Adami, because its 
flowers are barren, while the branches that revert to the yellow Laburnum 
produce seeds in the ordinary way. 
A final question remains for consideration, namely, the precise way in 
which the hereditary qualities are borne by the chromosomes, but this would 
lead us too far into the regions of speculation. The number of chromosomes 
among plants bears no definite relation to the number of characters 
possessed by the individual, being generally much fewer, and the loss of @ 
character does not involve the corresponding less of a chromosome. The 
question of chromosomic development is now being extensively investigated 
in connection with the origin of mutations, but the results, so far as we have 
been able to gather, do not throw much light upon the question of reversion 
among secondary hybrids. 
We are inclined to regard reversion as a mere accidental accompaniment 
of a fundamental process, a sort of by-product of sexuality due to imperfect 
blending or re-separation through incompatability of hereditary qualities 
derived from diverse ancestries. Sexuality arose directly from the earlier 
method of reproduction by vegetative bipartition, and as a means of 
recovering exhausted vitality, probably due to seasonal variation. At first 
a mere protective phase, the advantages secured by this combination of 
forces were such as to secure its continuance, and by progressive develop- 
ment under changing environment it has come to replace more and more 
the older method, while disadvantages have been got over by the disap- 
pearance of unsuccessful combinations under the evolutionary process. 
The nucleus of the vegetative cell gives rise to the reduced nucleus of 
the gametes in the germ plasm, and the gametes which unite to form the new 
individual may be those of the same or of a diverse species, according to 
opportunity. In the latter case a hybrid is formed, in which incompat- 
ability may manifest itself, and this would result in the production of 
gametes of diverse character when the germ plasm came to be formed, 
and their subsequent union in the sexual process would inevitably produce the 
phenomena of variation and reversion with which we are now so familiar ip 
batches of secondary hybrids. Species produce uniform gametes, hence the 
degree of uniformity seen among primary hybrids. R.A. 
