the Ascocarp in Mona sens. 221 
of the oospheres affording a link between the processes typical 
of spore-formation in sporangia and asci. It is true that it 
may be urged against this view that the oogonium is not 
homologous with the ascus or with the sporangium, and that 
if the two latter structures be regarded as truly homologous 
the gap between them remains therefore as wide as before ; 
but it is certainly shown that in some Oomycetes there exists 
a method of spore-formation, although not occurring in 
homologous structures, which is to some extent intermediate. 
Stevens (21) has shown that in Albugo Bliti , A. Portulacae 
and A. Ti'agopogonis the method of formation of the oosphere 
in the oogonium is as follows : — 
The protoplasm of this organ becomes much vacuolated, 
clumps of denser protoplasm being distributed irregularly 
among the more vacuolated substance. These clumps increase 
in size by fusion, and eventually a single dense mass, the 
gcnoplasm of De Bary, is formed in the centre of the oogonium 
surrounded by the vacuolated periplasm. The nuclei are at 
this stage arranged in a ring around the gonoplasm in the 
inner portion of the periplasm. They divide, and one or more 
of their daughter-nuclei enter into the gonoplasm and there 
fuse with the male nucleus or nuclei. It is remarkable that 
the sharp differentiation between the gonoplasm and the 
periplasm seems to be associated with the zonation stage of 
nuclear arrangement. Karyokinetic division of the nuclei 
occurs at this time simultaneously, and it seems as if this 
division has some connexion with the final cutting out of the 
oosphere. Perhaps the kinoplasm of the spindles acts in 
combination throughout the whole region of zonation and cuts 
out the compound oosphere in a manner somewhat similar to 
that by which the ascospores are cut out by the radiating 
kinoplasmic threads of the asters, which has been shown by 
Harper (11) to be typical of the formation of spores in asci. At 
any rate the processes are similar up to a certain point,- for in 
each instance the oosphere or the ascospores are formed from 
a dense protoplasmic mass which gradually collects at one point 
in the mother-cell and is distinguished from a differentiated, 
