256 THE GERM-PLASM 



one of the parent-species were large, and of a pale lilac colour, 

 while those of the other were smaller, and their colour was red, 

 with a dark crimson ground. The tiowers of the dit^erent 

 hybrids were by no means quite similar, but three principal forms 

 could be distinguished according to the combination of colours 

 in the flowers, which I shall not describe in detail : the flowers 

 of the same hybrid, ho^vever, resembled each other in their Jiiost 

 7ni?inte details. One plant, for instance, had violet petals of a 

 rather pinker tint than those of one of the parent-species, and 

 all the petals were strongly tinged with red on one and the same 

 lateral margin. As far as I could observe, all the flowers were 

 similarly coloured on this stock. On another stock, all the sepals 

 had brown rims, and on a third there was a narrow dark orange- 

 coloured band in the centre of each flower, /n these cases, there- 

 fore, the combination of the colours of the parents which appeared 

 in the petals of the hybrids must have been decided at the time of 

 fertilisation. It will be shown later on how this combination 

 may vary somewhat in difl^erent plants. 



Even although the slight differences in identical human twins, 

 which can be proved to exist, are certainly due in part to minute 

 differences in the idioplasm itself, some of them must neverthe- 

 less with equal certainty be attributed to the elTect of various 

 external influences. My photographs of the above-mentioned 

 identical twins show that No. 507 has particularly white hands, 

 while those of No. 508 are much browner. No one would 

 attribute this fact to dissimilarity in the respective germ-plasms, 

 or to an alteration in the proportion of paternal and maternal 

 idioplasm which occurred during ontogeny : it must be due to 

 the fact that the hands of No. 508 had been more exposed to 

 the sun than those of No. 507 ; and, as it happens, the former 

 of the two had been more employed in the open air than the 

 latter before the photograph was taken. Several diff"erences 

 in the proportional sizes of parts of the body may possibly have 

 been brought about in a similar wav. 



o 



2. The SH.A.RE TAKEN BY THE ANCESTORS IN THE 



Composition of the Germ-plasm 



If, then, it is certain that the characters of the developing 

 offspring are essentially decided by the mingling of parental 

 idioplasms which takes place in the process of fertilisation, we 

 must next try to ascertain whether the entire parental idioplasm, 



