Wilson: North American Peronosporales 
61 
stage the antheridium is the first to appear, and is often apparently 
fully developed before there is much evidence of the oogonium. 
Whether or not the peculiar swellings spoken of earlier develop 
into antheridia as a result of contact with certain other threads 
or swellings, it is difficult to determine, but it seems most probable. 
This potential oogonial thread, with or without a swelling, be- 
comes attached to the base of the antheridium and grows up along 
its surface toward the apex. Very often it can be seen when it 
has only partially covered the length of the antheridium. For a 
long time it was difficult to decide whether or not these threads 
did not actually penetrate the antheridium and grow through it, 
and we are not yet certain that this does not sometimes occur. 
Certainly the optical effect is frequently that of an internal thread 
with its apical walls very thin as compared with the side walls. In 
time, however, the oogonial thread reaches the top of the antherid- 
ium, and curving around its apex, begins to swell into the 
oogonium,' which by this time is usually cut off from its basal 
thread by a septum.” 
To judge from the later work of Pethybridge (1913) and the 
illustrations from photographs which accompany the later paper 
by Clinton it appears that what this author really saw and de- 
scribed was the same type of oospore formation as that recently 
described by Pethybridge and by Dastur, but that over-caution 
prevented him from making the proper interpretation of his 
observations. 
5. Phytophthora erythroseptica Pethyb. 
The announcement by Pethybridge (1913) of this fungus is 
interesting as adding one more to the already long list of Euro- 
pean diseases of the potato as well as including a second species of 
Phytophthora in the list. The fungus is doubly interesting as 
being the species for which was first described that peculiar 
method in oospore formation which we must now consider typical 
of the genus Phytophthora. 
So far as mycelial characters are concerned this species is not 
unlike other members of the genus. The conidia are similar to 
those of P. infestans, but larger and not so prominently papillate, 
although there is always a well-marked apical region with a 
