No. 463.) STUDIES ON PLANT CELL.— VI. 453 
upon information which in point of completeness falls very far 
short of our knowledge of the groups above. Indeed, no forms 
have been studied with the detail that is known in higher groups 
chiefly for the reason that the investigator is forced to deal with 
very small nuclei and mitotic figures whose chromosomes are 
exceedingly minute and because of various technical difficulties. 
The theories in general fall into two groups: (1) those which 
have an obvious basis in attempts to reconcile events with the 
processes of gametogenesis in animals, and (2) those proceeding 
from the view that for phylogenetic reasons the periods and phe- 
nomena of gametogenesis in the lower plants should correspond 
with those of the higher. 
We may pass over with a few words the early crude attempts 
to establish structures for plants comparable to the polar bodies 
of animals. For example at the conclusion of oögenesis in some 
algae (e. g., Vaucheria, CEdogonium) a globule of slime is exuded 
with the opening of the oógonium. It was suggested that such 
material is thrown off from the egg but we now know that it is 
not protoplasmic in character but is apparently derived from a 
softening of the cell wall. Then the ventral canal cell has been 
compared to a polar body but it seems clear now that all of 
the canal cells are homologous and a part of what was form- 
erly an extensive gametogenous tissue within the archegonium. 
Then the small group of cells cut off below the oógonium of the 
Charales and the fragmented nuclear material in the trichogyne 
of the red algze have been compared to substance thrown off 
from the egg but without any knowledge of the nuclear struc- 
ture. Finally the nuclear degeneration which is a very conspic- 
uous feature of oógenesis in certain groups whose oógonia are 
multinucleate (Peronosporales, Saprolegniales, Pelvetia, etc.) 
has been considered related to reduction phenomena. But the 
nuclei in all of these forms bear every evidence of being in each 
type homologous structures whose large numbers have a phylo- 
genetic raison d'étre and the extensive degeneration is associated 
with the principles of sexual evolution which tend to conserve 
protoplasm for the good of a lesser number of gamete nuclei 
even to the sacrifice of others that are potentially equivalent. 
We will now consider the few instances among the thallo- 
