Pollen Mother-cells of Li Hum canadense. 247 
higher animals and plants. In animals, each of these cells is a sexual cell 
destined to fuse with another, usually from another individual, and so 
to give rise at once to a new animal provided with the parental idioplasms. 
In the case of plants, the cells in question are asexual spores, which give 
rise to a new generation which in turn produces the sexual cells. Each 
cell of the generation produced by the germination of the spore is charac- 
terized, like the spore, by the presence of the reduced number of chromo- 
somes. The sexual cell ultimately produced by this generation, therefore, 
since it is descended directly from the spore through a series of cell divisions 
interrupted by no cell fusions, presumably resembles the spore in its idio- 
plasm content ; and therefore the generation produced by the fusion of two 
such sexual cells resembles the sexually-produced animal in its endowment 
of two separate idioplasms. Now it happens that in the Spermaphytes, 
which are the only types of plants to be considered in the present discussion, 
we are practically confined, so far as the study of hereditary characters 
is concerned, to the sexually-produced generation, the sporophyte, since the 
gametophyte, characterized by the possession of the reduced idioplasm, is 
in this group a very short-lived, few-celled generation. So far, therefore, as 
concerns the determination of the characters of the predominant phase 
in its life-history by two independent idioplasms, a Seed Plant essentially 
resembles one of the Metazoa. 
The observations of others, as well as my own, seem to show that the 
division of the chromatin in the homoeotypic mitosis is essentially similar, 
except for the reduced number of chromosomes, to that characteristic 
of somatic divisions. This being the case, it is in the first longitudinal 
splitting, which determines the grouping of the hereditary materials that are 
to be distributed in the heterotypic mitosis, that we must seek an explana- 
tion of the nature of chromosome reduction. 
The fusion of the two spirems and the subsequent splitting of the 
fusion thread may be imagined to produce any one of several different 
results, as regards the chromatin bodies within the threads, and these various 
possibilities will be considered separately. 
1 . There may be a complete fusion in pairs, not only of the chromo- 
meres and of their visible component granules, but also of the smaller units, 
if such there be, resulting in the production of a single idioplasm different 
from that of either parent. The subsequent fission of the thread must then 
be equational, since any other method of division would result in germ-cells 
each provided with only a partial set of idioplasmic structures, and hence, 
so far as we can judge, incapable of giving rise to a complete individual. 
Such an entire fusion of the parental idioplasms was postulated by Stras- 
burger (’94), and is, indeed, so far as I can see, the only hypothesis which is 
compatible with the notion of the universal occurrence in all mitoses 
(including the heterotypic) of an ‘ equation division.’ Hertwig (’90) also 
