PREFACE. 



This volume presents the subject of fecundation in the vegetable 

 kingdom by the discussion of concrete cases, selecting from the great 

 groups of plants certain typical representatives in which the sexual 

 process seems to have been most thoroughly investigated. In the 

 introductory chapter I have discussed typical processes of nuclear 

 division and cell-formation, especially in spore mother-cells, together 

 with a few topics dealing with certain phenomena of the cell and the 

 significance of sexuality. This is considered necessary to a better 

 understanding of sexual reproduction, for problems of sexuality, like 

 problems of evolution, have in late years become reduced to problems 

 of the cell, and, since the nucleus plays by far the most important 

 part in fecundation, I am tempted to say to problems of the nucleus. 



The processes leading to the development and differentiation of the 

 gametes have been regarded as of prime importance, and they have 

 therefore received emphasis. Whenever the subsequent history of the 

 fecundated egg has been followed to any extent this has been done, as 

 in the Ascomycetes and Floridece, to show the relation between the 

 real sexual process and the vegetative fusion of nuclei which has been 

 confused with the sexual act, and, as in the Desmids, for the sake of 

 pointing out certain nuclear phenomena that take place during the 

 germination of the zygote with similar phenomena just preceding the 

 sexual act in the Diatoms. Processes which are purely morphological 

 are assumed or dealt with very briefly. 



In grouping the representative types into the several chapters I have 

 had in mind no particular theory of the evolution of sexuality, but 

 merely the idea of the evolution of the plant kingdom and the corre- 

 sponding differentiation of the sexual organs and cells accompanying 

 this evolution in the groups of plants themselves. 



The chapters dealing with the lower plants in which the develop- 

 ment of the gametes is not known from a modern cytological standpoint, 

 and in which the behavior of the sexual nuclei in the fusion of the 

 gametes has not been followed have been made as brief as possible. 

 For a similar reason the mosses and liverworts have been omitted 

 entirely. 



