376 METAMORPHOSIS 



the cause of the more vigorous growth of the hybrid. This releasing stimulus 

 may reside in a soluble chemical compound. We have already often spoken of 

 stimulation of growth by ' poisons ', and we may compare the poisonous 

 effects of the action of copper-sulphate and other chemicals with the effect 

 of hybridization, for there, as in hybrids, we may often have, side by side, an 

 increase in vegetative growth and an inhibition of the formation of reproduc- 

 tive organs (compare pp. 88 and 374). Such facts as these, viz. that widely 

 separated races produce weak-growing hybrids, that more widely separated forms 

 do not hybridize at all, and that the pollen of a race still more distantly 

 related may even injure the stigma of another form, recall at once the action 

 of poisons [comp. DARWIN, 1868, II, 180]. 



In addition to the incentive to growth, fertilization leads to the fusion of 

 two different protoplasts, each having their individual initials. What 

 do hybrids teach us in this relation ? It is perfectly obvious that such a 

 combination occurs but we have nothing to go upon to enable us to determine 

 what will be the primary result of this union. On account of the varied be- 

 haviour of the hybrid we can say nothing as to whether a form will arise inter- 

 mediate between the two individuals, whether the differences will be neu- 

 tralized and the species remain constant or whether on the contrary new types 

 will appear and maintain themselves and the species become polymorphic. 



Although hybrids dp not at present throw light on the problems as to the 

 significance of fertilization, they are nevertheless of primary importance in 

 another important question, i.e. heredity, the phenomenon of the handing on of 

 the parental characters to the offspring. Heredity is a peculiarity of organisms 

 which is shown both in the simplest form of reproduction, i.e. fission, and in 

 the most complicated sexual process, but although in the first case it may be re- 

 garded as a matter of course, in the latter it is an extremely wonderful pheno- 

 menon. Considering, e.g., division in the cell oiSpirogyra, the protoplasm, the 

 nucleus, and the chloroplasts divide, and these products of division have the 

 power of growth. Now if new characters appeared in these two halves which 

 were not present in the parent it would be a much more wonderful fact and one 

 much more difficult of explanation than if each half had the peculiarities of the 

 whole as is, as a matter of fact, the case. If we consider now a complicated 

 plant, such as a mushroom or a moss, we find there single cells the spores 

 capable of giving rise to a new organism similar in all respects to the parent. 

 In each spore the initials of the whole organism must be present and there 

 must also be arrangements for the development of these initials in the way 

 characteristic of the organism in question. Looking at sexual reproduction 

 only we have seen clearly from our study of hybrids that in both sex-cells the 

 initials of an entire organism are present, and hence that the fertilized ovum 

 contains the initials of two organisms although only 'one results. Since in 

 certain cases it may be clearly proved that these initials do not unite later on, 

 we arrive at the conviction that in each sexually-produced plant there are 

 many initials which do not develop but remain latent. 



It is impossible for us at present to deal with the problem of heredity in all 

 its bearings, all we can do is to treat of it briefly in so far as it is elucidated by 

 fertilization and hybridization. Let us direct our attention in the first place to 

 the question of the material basis of heredity. 



In the division of Spirogyra no special theory need be referred to. All the 

 organs of the daughter-cell are parts of corresponding organs of the mother-cell ; 

 the nucleus inherits qualities of the nucleus, the chloroplast those of the chloro- 

 plast, and so on. Let us compare with this case the development of the flowering 

 plant from the ovum, and confine ourselves at first to the individual cells which 

 arise from it. The protoplasm and the nucleus of each of these are also deriva- 

 tives of the plasma and the nucleus of the egg, and we may therefore admit at once 

 that all the peculiarities of protoplasm, and all the peculiarities of the nucleus 



