I }4 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 periplasm, which may easily be overlooked (Fig. 61 //, 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 n). 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 

 air 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 fertilisation-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 1 ontents. The oosphere at once becomes inv< 

 with a thick cellulose-membrane and ripens into the oospore (Fig. 61 III— VI). In the 

 genus Phytophthora the process is in every respect the same as in Pythium, except 

 that only a very minute quantity of protoplasm parses 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 b( rved are essentially the same as in the two preceding 



