1889.] BOTANICAL GAZETTE. 55 



sented by separate particles of living matter. Of these there 

 are as many kinds as there are characters, and Darwin has 

 called them " gemmules." Their principal attributes are 

 that they are capable of growth and reproduce themselves, 

 and that they can remain latent for a long time, even during 

 many generations. In this case the hereditary characters 

 with which they correspond do not become visible, but after 

 a certain time they may reappear. When cell-division takes 

 place, the gemmules are equally divided in the two nascent 

 9 cells, and this is one mode of migration, by which the sev- 

 eral organs and tissues of the body acquire their hereditary 

 characters. 



2. There is still another mode of migration, as it is assumed 

 that every separate part of the whole organization throws oft' 

 its gemmules, which are dispersed throughout the whole sys- 

 tem, and are collected from all parts to constitute the sexual 

 elements and buds, from which new beings are developed. 



The second position was much insisted upon by Darwin, 

 as he thought this assumption necessary to explain the he- 

 reditary effects of use and disuse, the occurrence of graft- 

 hybrids, and the direct action of the male element on the 

 female. 



Our views upon this part of the subject have been much 

 changed since Weismann 3 has shown that those cases in 

 which characters, seemingly acquired in later life, are trans- 

 mitted to the offspring, do not necessarily prove a transmis- 

 sion of these characters from the altered organs to the germ 

 which will become a new individual. They can be explained 

 as well by assuming that the peculiar structure of the germ f 

 from which the first varying individual sprung, caused the 

 subsequent variations also, and that they were thus trans- 

 mitted from germ to germ. 



Hence there remain only a few, seldom occurring cases, 

 which seem to be inexplicable, if migration of gemmules is 

 not conceded. But as some of these cases can be explained 

 otherwise, and all stand in need of further investigation, there 

 are now no sufficient reasons to support the theory that gem- 

 mules migrate from all parts of the organism in order to 

 unite in some other parts. 



Those authors, however, who are opposed to the migra- 

 tion theory, have mostly thought that with it the whole hy- 

 pothesis of pangenesis fell. But this, obviously, is a grave 

 error, as the first and essential supposition of the hypothesis 

 remains unshaken by these arguments. 



a Ueber die Vererbung, 1883. 



