CHAPTER V.—-COMPARATIVE REVIEW.—SAPROLEGNIEAE. I4I 
SAPROLEGNIEAE. 
Section XL. These plants, which live on dead organic bodies in water, closely 
resemble the Peronosporeae in the course of their development and to some extent 
also in habit; they are most of them of large growth, with tubular hyphae 1-2 cm, in 
length standing out from the substratum and slender rhizoids spreading through it 
(Fig. 68). They differ from the Peronosporeae chiefly in the development of the 
oosphere and in the circumstance that in all the better-known species the antheridia 
though existent do not perform their fertilising function, or are entirely wanting. 
The oogonia are formed on branches of the thallus-tubes as in the Peronosporeae, 
and the whole of the fatty protoplasm is transformed into a single oosphere, or divides 
into several portions which become so many round oospheres, without any separation 
of periplasm. The number of oospheres varies in both species and individuals. Most 
species have as a rule several oospheres in an oogonium, some have as many as 30 or 
40 or more, feeble specimens often only 
2-4. The oospheres ripen into oospores, 
which in most cases have the same struc- 
ture as those of the Peronosporeae, es- 
pecially the Pythieae (Fig. 69 C). A few 
species are unlike the rest in this respect. 
Like the Peronosporeae many Sapro- 
legnieae have antheridia ; in a few species 
only (Saprolegnia hypogyna, Pringsh.) the 
antheridium is the stalk-cell which bears the 
oogonium, as in Monoblepharis (Fig. 67): 
usually it is the obliquely club-shaped or 
cylindrical terminal cell of slender branches 
which grow one or more in number to- 
wards the oogonium and apply themselves ; 
‘ ER FIG. 68. Achlya prolifera. A germ-plant twenty-four 
elect Wei ab Thee Teed en ne re mee 
branches spring, according to the species, — branches of the primary rhizoid which have penetrated into 
either from the branch of the thallus Br ra tae as tie Saba Hana GE an aoe ete 
J sequently fertile branches. 
that bears the oogonium to which it at- 
taches itself, and then usually close to it 
(androgynous forms; Fig. 69 A, 2); or from special branches of the thallus which 
do not bear oogonia (diclinous forms); cases intermediate between the two extremes 
are of comparatively rare occurrence. The antheridial branches apply themselves to 
the oogonia. The first appearance of the lateral branches and the delimitation of 
the antheridia take place before the formation of the oospheres. When these are 
formed, the antheridia usually send out 1, 2, or 3 delicate tubular processes which, like 
the fertilisation-tubes of Pythium, grow into the oogonium and in the direction of the 
nearest oosphere and apply their apex firmly to it; but they do not open, and 
nothing like a discharge of their protoplasm has ever been observed (Fig. 69 2); on 
the contrary they generally continue to elongate after their first contact with an 
oosphere and grow over its surface and not unfrequently beyond it. When there 


