246 BOTANICAL GAZETTE [OCTOBER 
developing papilla, and exhibits a granular cytoplasm at this 
point. The granulation probably indicates the presence of a 
cellulose enzyme, formed here to soften the wall which alters 
chemically, as is evidenced by its response to stains and by its 
swollen condition (Stevens 1899, figs. 47, 50). The antheridial 
tube at this stage of development is probably unable to pene- 
trate the cellulose wall of the oogonium, and that duty rests 
with the female cell. 
Perhaps this curious structure can better be interpreted by a 
glance at possible ancestral forms. In algal aquatic forms, in 
which the gametangia open into the water, each sex organ opens 
independently, the female usually first. If the Peronosporeae 
have been derived from some such ancestors and these habits 
have been retained, in species where the walls of the antheridium 
and oogonium are in contact the origin of the receptive papilla 
is clear. Gametangia are usually of greatest turgor at the time 
of opening; therefore, in the present case the bulging, conse- 
quent upon the softening of the partition wall, is from the 
oogonium toward the antheridium. The formation of the recep- 
tive papilla in Albugo occurs immediately before the maturity 
of the oosphere, precisely as does the analogous phenomenon in 
Vaucheria. 
~The term ‘receptive papilla”’ is a misnomer, since this is not 
in any morphological sense a receptive structure, nor is it homol- 
ogous with the receptive spot of the egg. In one case the 
differentiated area is part of an egg and functions as a place of 
reception for the sperm (as the eggs of Sphaeroplea, Sapro- 
legnia, Oedogonium, etc.); in another case it is a zymogenic 
region of the protoplast adjacent to the point where an opening 
is to be made in an oogonial wall, either to furnish exit for the 
female gametes or for the entrance of the male elements, and is 
homologous with the opening spot of sporangia generally, as 
Cladophora, Bryopsis, Sphaeroplea, and Oedogonium. In the 
Saprolegniaceae the papilla does not furnish the place of 
entrance for the antheridium tube, although in Albugo it does 
(Zopf 1890, p. 293). The two regions occasion no danger of 
