3« i 
Physiology of the Saprolegniaceae. 
that the results of Klebs, Davis, and myself on the variability of Saprolegnia 
mixta or of any of its forms, in obtaining cultures which produce no 
antheridia, warrant the view that this condition represents Saprolegnia 
ferax . This species, it is true, is said to have no antheridia ; but any one 
who has seen the true 5 . ferax (S. Thureti ) will remember some very 
essential characters which always stand out in fly cultures of this species. 
One of these is the presence of large cylindrical oogonia with the oospores 
in a single row. Humphrey has expressed himself forcibly on this point: 
‘The rather common occurrence of cylindrical oogonia and the very con- 
spicuous pitting of the oogonia mark this species unmistakably.’ 
With reference to the variability of Saprolegnia hypogyna there are 
several points that need attention here. I have already fully indicated 
some lines of variation. Now if these variations could be fixed, the result- 
ing forms would be similar to the varieties of N. hypogyna described and 
figured by Maurizio ( 94 ). According to him, all his varieties agree with 
De Bary’s N. hypogyna in the following characters : firstly, the hypogynous 
antheridial cell ; secondly, the centric oospheres ; thirdly, the flask-shaped 
oogonia. The oogonia of my plant were globular, which according to 
De Bary’s original description (’88), is one of the shapes. In his ‘ variety I ’ 
the antheridial cross-walls are nearly always wanting — a phenomenon also 
noticed in some of my cultures — the oogonial stalk is variously bent, and the 
pits project somewhat above the surface of the oogonium— also noted in 
my cultures. In his ‘variety II’ the characters are: many pits, straight 
stalk, and additional cross-walls on the oogonial stalk. In my cultures the 
pits were found to vary in number and size, and additional cross-walls 
on the oogonial branch were common in calcium phosphate solution, as 
shown in Fig. 9. His ‘variety III ’ is like his II except the additional cross- 
walls, and in its short protuberances on the side of the hypogynous cell. 
Here, then, is a form found in nature with all the characters of those 
forms which I succeeded in getting in cultures with CaHP 0 4 , as shown in 
Figs. 5, 6, and 7 (compare also Fig. 20, Pis. IV and V, Maurizio, ’ 94 ). In 
both the side-branches have attained only partial development, as no 
antheridia are cut off from them. The hypogynous cell is usually empty, 
as is also the tube which pushes up into the oogonial wall in some cases ; in 
fact so much alike are his ‘ variety III ’ and my cultural form that it is difficult 
to select differences, the number and size of pits seeming to be the only 
differing character. 
Maurizio’s ‘ varieties IV and V ’ are characterized by the few pits ; 
the former also by the thin oogonial wall, and the latter by the presence 
of definite protoplasm within the projection of the hypogynous cell where 
it pushes into the oogone ; both lack side-branches. No especially thin 
walls were noticed in the oogonia of my cultures. The presence or absence 
of a healthy-looking protoplasmic content of the projection certainly varied 
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