134 DIVISION II.—COURSE OF DEVELOPMENT OF FUNGI, 
A slowly progressing separation begins in the protoplasm soon after the delimitation ; 
the denser protoplasm with the oil-drops moves from the wall to the centre of the 
oogonium and aggregates there into a smooth globular body, the oosphere, which 
is surrounded by a delicate hyaline pellicle. The space between the oosphere 
and the wall of the oogonium continues to be filled with a slightly granular hyaline 
protoplasm, the ferzplasm, which may easily be overlooked (Fig. 61 JI, III). 
About the same time that delimitation of an oogonium takes place the formation 
of at least one antheridium begins close to it (Fig. 61; see also Fig. 62 2). The 
antheridium is in the simplest case a younger sister-cell of the oogonium formed 
by delimitation of the contiguous portion of its parent-filament; terminal oogonia 
are therefore placed upon it as on a stalk-cell, which may either remain straight 
(Fig. 67) or have a characteristic curvature. In another series of cases the anthe- 
ridium is the terminal cell of a special branch of the thallus, which grows towards 
the oogonium and attaches itself firmly to it; and this branch either springs from 
the same filament as the oogonium for which it is provided and close to it, bending 
over towards it, or it proceeds from some other branch of the thallus lying near 
the one which bears the oogonium. These circumstances of form and insertion vary 
sometimes in different species, sometimes in different individuals; so also the 
number of antheridia attached to one oogonium, which are often two, but in P. 
megalacanthum may be as many as six. 
The cell-wall of the antheridium is not thickened, and its protoplasm is at 
first parietal and granular and not distinguishable from that of the thallus. When 
the oosphere has been formed in the oogonium, the antheridium sends a delicate 
cylindrical or conical tube-like process, the /erzilisalion-tube, from the part of its 
surface which is in contact with the oogonium into the interior of the latter; the 
tube grows till it reaches the surface of the oosphere, attaches its apex firmly to 
it and subsequently opens at that spot. Soon after the formation of the tube the 
protoplasm becomes differentiated in the antheridium; the larger and denser 
granular portion moves into the centre of the cavity, forming there an irregular and 
somewhat indistinct strand, the gonoplasm, while a thin layer (periplasm) remains on 
the wall of the cell. Then the gonoplasm passes slowly in most cases through the 
fertilisation-tube which has opened in the meanwhile into the oosphere, the transference 
of the whole of the gonoplasm being completed in from one to two hours. If there 
is more than one antheridium, they all usually, but not always, empty their gonoplasm, 
one after the other, into the oosphere. At least one antheridium discharging 
its contents in this way is invariably present on normal specimens, that is to 
say, on those which develope an oosphere. The function of the antheridium is 
fulfilled when it has discharged its contents. The oosphere at once becomes invested 
with a thick cellulose-membrane and ripens into the oospore (Fig. 61 ZZ/Z-VI). Inthe 
genus Phytophthora the process is in every respect the same as in Pythium, except 
that only a very minute quantity of protoplasm passes over into the oosphere through 
the fertilisation-tube, and this portion is not distinctly separated beforehand. Phyto- 
phthora omnivora has one noticeable peculiarity; the oogonium and its antheridium 
are formed almost simultaneously beside one another and develope in connection 
with one another. In Peronospora again such phenomena of development and 
fertilisation as can be observed are essentially the same as in the two preceding 
