Lal 
1905) CHAMBERLAIN—ALTERNATION OF GENERATIONS 14 
reduced condition. In many gymnosperms the vegetative tissue has 
become reduced to two evanescent ‘‘prothallial” cells, and even these 
are lacking in mostforms. In the angiosperms it is only rarely that a 
vestige of the vegetative tissue in the form of a prothallial cell is found. 
The formation of a tetrad of spores 
seems to be universal. The interval 
between the reduction of chromosomes 
and the formation of the sperm is gradu- , a 
ally reduced, until in the angiosperms 
there are only four mitoses in the game- (|e) 2) 
tophytic generation. 
I believe that the condition which pre- B B 
vails in angiosperms is directly compar- 
able with that found in animals. This 
comparison is illustrated in the accom- 
panying diagram (fig. 2). Here again . 
the plant shows a slightly more extended () (0) (0) (o) 
development, the condition shown in E CO} (o}(2) 
of the diagram having no parallel in ani- 
mals. But, as in the case of the female 
gametophyte, the objection is not serious, : 
for the male gametophyte has been gradu- ae 
ally reduced from a conspicuous, inde- ad 
pendent plant to a microscopic, parasitic Fic. 2.—A-E, spermato- 
structure with only three nuclei. Itis not genesis in an angiosperm. 4, 
at all improbable that instances will yet 
be found in which the last two mitoses nuclei in Erepresent the sperm 
have been suppressed, the microspore nuclei, the unshaded nucleus 
functioning as a sperm. This condition 
could then be illustrated by E in the ie B’-D’, succeeding stages; 
diagram. the reduction of chromosomes 
The sporogenous tissue which pre- ee eae me soa 
cedes the formation of megaspore mother- = 
cells and microscope mother-cells is comparable with the oogonia and 
Spermatogonia of animals. Preceding the formation of megaspore 
mother-cells this tissue becomes much reduced in the higher plants 
and in many cases is altogether lacking. 
