238 PUYTOPHTHORA ON VINCA ROSEA 



The swollen or knob-like portion of the oogonial incept that is outside the 

 antheridial incept may give out a sterile projection like the antheridium. 

 lu a few cases two oogonial incepts have been found to penetrate the same 

 antheridium at two different points, but these oogonial incepts have never 

 been found to mature ; they were never observed to break through the antheri- 

 dium. It is quite possible for more than one oogonium to be attracted towards 

 a single antheridium and to make their way within it ; but it is a question 

 whether the antheridium would be able to fertilize more than one oogonium. 

 The oogonial incept within the antheridium is club-shaped, grows within it 

 and eventually bursts through it at some point. In an exceptional case the 

 oogonial incept within the antheridium had made attempts to break 

 through at four places by means of four projections three of which 

 had succeeded in boring their way out (Fig. 8). In another case the oogonial 

 incept within the antheridium bifurcated before leaving it and two branches 

 made their way out by piercing the antheridial wall at two different points 

 (Fig. 9). It seems improbable that these oogonia would ha\e matured and 

 produced oospores. After leaving the antheridium, the oogonial incept 

 swells out into a globose body, the oogonium pioper. The course of develop- 

 ment of the oospore could not be observed. For the asexually formed sporangia 

 to revert to the vegetative condition is common and cases have also been known 

 in some species of Pythivm, where the oogonium had also reverted to the 

 vegetative condition. Thus Wahrlich^ has observed oogonia, which, on 

 being not fertilized, continue their growth vegetatively. Ward^ has also 

 made like observations. A similar case has been found in the fungus under 

 study (Fig. 10). An oogonium in Oat juice agar, after making its way out 

 from within the antheridium, had grown to its full size but the wall was still 

 unthickened and uncoloured ; it was almost empty of its protoplasmic contents, 

 except the thin layer that lined the inside of the oogonial wall and the little 

 mass that was at the base of the oogonium. Within the antheridium a lateral 

 branch had grown out piercing the antheridial wall. Outside the antheridium 

 it became septate and the portion beyond the septum had protoplasmic con- 

 tents finely granulated and was thin- walled, like an ordinary hypha, while 

 that below the septum was empty and slightly thicker, as thick as the oogonium 

 from which it had arisen ; it also contained a small cellulose ingro\\-th. The 

 oogonium on failing to form an oospore had thus germinated vegetatively. 

 The colour, thickness, and size of the oogonial wall is influenced by the medium 



I Wahrlich, W. Pythium n. sp. Ber. Deut.^ch. Bot. Oes., V. 1887. 



i Ward, H. M. Observations on the genus Pylhium. Quart. Journ. Micros. Science, 

 XXIII (N. S.), 1883. 



