5 ( J4 THE GENESIS OK NEW SPECIES. 



they germinate. The variation is limited, it is true, to the different degrees in 

 which the seedlings resemble one or other of the parent-plants. If the cross is 

 between two plants of the same species no such variation can occur, seeing that the 

 plants crossed are alike in form. But there is still the question whether differences 

 in the age, size, and luxuriance of growth of the individuals which cross may not 

 have some influence on the result. So far as my experiments show, these differences 

 have no effect on the genesis of new forms, and have no prospect of becoming per- 

 manent characters in the offspring. A poor stunted plant growing on dry soil may 

 produce seeds which, on being planted in a good moist soil give rise, under favour- 

 able conditions, to well-developed plants capable of flowering luxuriantly. As is 

 well known, the first flowers of an inflorescence are always much larger than those 

 which subsequently open at the apices of the spike or raceme, or on the ultimate 

 ramifications of the cyme as the case may be. Now, if the large earliest flowers 

 are crossed one with another, and likewise the small latest flowers, and the seeds so 

 obtained in each case are kept separate but reared under similar conditions, the 

 plants produced from them do not differ in the slightest degree from one another, 

 but in their turn bear flowers, of which the first are the largest and the last tin- 

 smallest. Notwithstanding these results, however, I should not like, without 

 further investigation, to deny the possibility of the specific constitution of the 

 spermatoplasm undergoing some change as a result of external influences in the 

 course of its development, whether during its imprisonment in anthers or antheridia 

 or on its way to the ooplasm, or to say such change might not cause the descendants 

 of the plants concerned to differ in form from the individual from which they 

 sprang. 



It has been established beyond all doubt that modifications of form directly 

 induced by conditions of soil or climate are not hereditary, and that every change 

 of form which persists in the descendants is only brought about as the result of a 

 process of fertilization, or, in other words, that new species can only arise through 

 fertilization. Herein lies also the solution of the marvellous phenomenon known as 

 the alternation of generations, and of the question why plants in general flower and 

 undergo fertilization. To these processes is due the genesis of new species. The 

 propagation of plants, their multiplication and dispersal, may also be effected by 

 means of brood-bodies, and as a matter of fact these processes are continuously 

 operating on a vast scale. But the plants reproduced by brood-bodies retain the 

 form of their ancestors unaltered, and no new forms arise in this way. Suppose 

 that a locality is occupied exclusively by plants which multiply by brood-bodies 

 only and do not change their form, and that in consequence of a change in the 

 climate such species as are not adapted to the new conditions abandon their homes, 

 or else languish and die out, the probability is that many of the vacated spots will 

 remain unoccupied owing to there being no recruits in the neighbourhood, or from 

 out its confines, that are better adapted to the new conditions. If, on the other 

 hand, the area in question is inhabited by plants which reproduce sexually and 

 which, by crossing one with another, produce descendants of diverse forms, there is 



