Harper. — Cell- Division in Sporangia and Asci. 471 
toward which the protoplasm of the wall-layer is drawn 
together. 
He notes very clearly a preliminary contraction followed 
by swelling, and a second final contraction of the spore 
masses. 
Berthold 1 regards the process of cleavage in Saprolegnia 
as derived from free cell-formation and as representing a 
higher stage of development than the latter, since, in this 
case, the spores are able to separate out of the parent plasm 
and maintain their independence without the sacrifice of 
materials involved in the formation of periplasm. This view 
involves of course a reversal of the process as conceived by 
Brefeld, who holds that the ascus has been derived from the 
sporangium. The sporangium, according to Berthold’s view, 
has been developed from types which form periplasm rather 
than the reverse. The ascus being in the latter group repre- 
sents the more primitive type. It is to be noted that, while 
insisting definitely on the derivation of the sporangium as 
seen in Saprolegnia from some periplasm-producing type, 
Berthold does not go into the question of establishing 
relationships between the groups of fungi on this basis, his 
interest in the matter being wholly from the mechanical 
physiological standpoint. Berthold^s doctrine of the strati- 
fication of the cell-body, with polarity determined by the 
position of the nucleus, influences throughout his interpreta- 
tion of the spore-formation in the sporangium. Also the 
position of the developing oosphere, he thinks, is determined 
by the appearance of certain new and characteristic relations 
in the symmetry of the wall-layer of the oogonium. 
The differentiation of the sporangium-contents into a central 
vacuole and a peripheral protoplasmic layer is perhaps an 
example of stratification in a cell. The position of the 
forming spores is ultimately determined, as we shall see, by 
the position of the nuclei. Whether the distribution of the 
nuclei is influenced by diffusion streams, I shall discuss more 
fully later on. 
1. c. pp. 313-4. 
