388 



PROVISIONAL HYPOTHESIS 



Chap. XXVII. 



As, during all the stages of development, the tissues of plants 



a« tiaw p,p,11s are not known to be formed 



of 



and 



betwee 



dently of, pre 



cells 



elude that the gemmules derived from the foreign pollen do not 

 become developed merely in contact with pre-existing cells, but 



tually penetrate the 



cells of the mother-plant 



process may be compared with the ordinary act of fertilisation 



of the pollen-tubes penetrat 

 closed embryonic sack within the ovule, and determine the 



during which the contents 



e 



elopment of 



embr) 



According to this view, the cells of 



the mother-plant may almost literally be said to be fertilised by 

 the gemmules derived from the foreign pollen. With all organ- 

 isms, as we shall presently see, the cells or organic units of 

 the embryo during the successive stages of development may in 

 like manner be said to be fertilised by the gemmules of the 

 cells, which come next in the order of formation. 



Animals, when capable of sexual reproduction, are fully 



developed, and 



cely possible that the male element 



should affect the tissues of the mother in the same direct manner 

 as with plants; nevertheless it is certain that her ovaria are 

 sometimes affected by a previous impregnation, so that the 

 ovules subsequently fertilised by a distinct male are plainly 

 influenced in character ; 

 pollen, is intelligible through the diffusion, retention, and action 

 of the gemmules included within the spermatozoa of the pre- 



and this, as in the case of foreign 



vious m 



ale. 



Each organism reaches maturity through a longer or shorter 

 course of development. The changes may be small and insen- 

 sibly slow, as when a child grows into a man, or many, abrupt, 

 and slight, as in the metamorphoses of certain ephemerous insects, 

 or again few and strongly marked, as with most other insects. 

 Each part may be moulded w 

 corresponding part, and in this case it will appear, falsely as I 

 believe, to be formed from the old part ; or it may be developed 

 within a wholly distinct part of the body, as in the extreme 



thin a previously existing and 



of metag 



An eye, for instance, may be developed 



t where no eye previously existed. We have also see 

 ed organic beings in the course of their metamorphose 



nearly the same structure after passin 



sometimes attain 



O' 







