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 Florddee, 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 belek 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. 
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