252 BOTANICAL GAZETTE [OCTOBER 
of the oosphere without emptying, the stimulating agent pre- 
sumably passing through the wall of the tube when this becomes 
very thin. The conditions justify the hypothesis that the proto- 
plasm of the oogonium, or the periplasm as the case may be, 
contains the food constituents needed for the rather extensive 
production of the pectiniferous deposit, and that the substance 
contributed by the antheridial tube is more properly comparable 
to an enzyme than a food. It is a stimulant to activity rather 
than a material to act or to be acted upon. The protoplasm of 
the antheridium of Albugo, moreover, seems never to produce 
pectin, thus favoring the hypothesis that the necessary food 
materials are limited to the protoplasm of the oogonium. 
The antheridial tube in normal conditions opens near the 
center of the oosphere, from whence the stimulating agent 
diffuses outward, awakening no response in the ooplasm because 
this is incapable of response. When this stimulating agent 
reaches the oospheric plasmoderma it meets the periplasm, 
which immediately lays down the rudiment of the outer wall. 
The fact that the tube opens in the center of the oosphere 
explains the absence of pectin formation in the periplasm, since 
the large area of the oospheric plasmoderma is ample to receive 
all the pectin that is to be laid down. Moreover, the thickening 
wall probably retards the passage of the stimulating agent into 
the periplasm, so that the peripheral portion of the periplasm 
is not incited to formation of the pectiniferous layer, and there- 
fore the oogonial wall receives no pectiniferous coat. An 
answer to the question originally propounded by Cornu (1872) 
“si ce plasma extérieur a la propriété de se déposer en couche 
membraneuse, sans étre élaboré au préabable, pourquoi ne se 
dépose-t-il pas aussi sur les parvis d l’oogone ?”’ is thus sug- 
gested. 
Normally it is the periplasm that responds to the stimulus, 
and the periplasm is bounded by its own plasmoderma and con- 
tains its own nuclei. It is an independent unit distinct from the 
oosphere, although it is destined to sacrifice itself for the pro- 
tection of the oospore in a manner analogous to the tapetal 
