374 PROVISIONAL HYPOTHESIS Chap. XXVIL 



many molecules go to the formation of a genramle ; but when we 

 "bear in mind that a cube of - l0 l 00 of an inch is much smaller 

 than any pollen-grain, ovule or bud, we can see what a vast 

 number of gemmules one of these bodies might contain. 



The gemmules derived from each part or organ must be 

 thoroughly dispersed throughout the whole system. We know, 

 for instance, that even a minute fragment of a leaf of a 

 Begonia will reproduce the whole plant ; and that if a fresh- 

 water worm is chopped into small pieces, each will reproduce 

 the whole animal. Considering also the minuteness of the 

 gemmules and the permeability of all organic tissues, the 

 thorough dispersion of the gemmules is not surprising. That 

 matter may be readily transferred without the aid of vessels 

 from part to part of the body, we have a good instance in a 

 case recorded by Sir J. Paget of a lady, whose hair lost its 

 colour at each successive attack of neuralgia and recovered it 

 again in the course of a few days. With plants, however, 

 and probably with compound animals, such as corals, the 

 gemmules do not ordinarily spread from bud to bud, but are 

 confined to the parts developed from each separate bud ; and 

 of this fact no explanation can be given. 



The assumed elective affinity of each gemmule for that par- 

 ticular cell which precedes it in due order of development is 

 supported by many analogies. In all ordinary cases of sexual 

 reproduction, the male and female elements certainly have a 

 mutual affinity for each other : thus, it is believed that about 

 ten thousand species of Composite exist, and there can be no 

 doubt that if the pollen of all these species could be simul- 

 taneously or successively placed on the stigma of any one 

 species, this one would elect with unerring certainty its own 

 pollen. This elective capacity is all the more wonderful, 

 as it must have been acquired since the many species 

 of this great group of plants branched off from a common 

 progenitor. On any view of the nature of sexual repro- 

 duction, the formative matter of each part contained within 

 the ovules and the male element act on each other by some law 

 of special affinity, so that corresponding parts affect one 

 another ; thus, a calf produced from a short-horned cow by a 

 long-horned bull has its horns affected by the union of the 



