Pethybridge — On the Rotting of Potato Tuhers. 543 



in close proximity to one another as is the ease with certain species of 

 Phytophthora, such as P. Fngi, &c. 



In their very earliest stages of development these organs do not appear 

 to differ markedly from numerous other short outgrowths from the hyphae, 

 which, however, do not develop further, or produce only branches of the 

 mycelium, or, at any rate, do not become antheridia or oogonia. Such small 

 outgrowths are plentiful at certain stages in the growth of the mycelium, and 

 it seems probable that many of them may be tentative oogonial incepts, 

 which, in the absence of the necessary antheridia (the number of which seems 

 to be more restricted), do not develop further. 



The antheridium is always formed before the oogonium develops. It is 

 most frequently an oval or rounded structure borne laterally ou a liypha 

 from which, at any rate at first, it is not shut ofE by a septum, altliough 

 as a rule later on a transverse wall is formed. In some instances the antheri- 

 dium might be described as an intercalary growtli on a hypha, and in 

 such cases it becomes shut off from the latter by two cross- walls. At otlier 

 times the antheridium is formed at the extremity of a hypha and also 

 eventually becomes shut off by a transverse septum from the latter. The 

 antheridium becomes filled with a mass of granular protoplasm mpre dense 

 than that of the liypha which bears it, and ultimately this hypha and others 

 to which it is connected may become completely empty. 



The oogonial incept may also be either lateral, intercalary, or terminal. Its 

 free end appears frequently, if not always, to be somewhat swollen or knob- 

 like, and it is usually somewhat enlarged at its base, wliere it is attached to the 

 hypha bearing it, or, if intercalary, the hypha itself is swollen at this point. 



If the oogonial incept comes into contact with an antlieridium, it enters 

 into the interior of the latter, usually penetrating somewhere at or near the 

 base. If the oogonial incept dees not meet with an antheridium, development 

 appears to be checked, and, at any rate, no oogonium is formed. Fig. 11, 

 Plate XLIV, shows clearly an intercalary antheridium into which the free 

 end of a laterally formed oogonial incept has penetrated at a point low down 

 on one side. 



For exactly how long a time the apex of the oogonial incept remains 

 within the antheridium, and whether fertilization occurs or not at this stage, 

 are points which have not yet been determined. At the conclusion of this 

 period, however, which at the most can only be a matter of a few hours, and 

 is perhaps less, the oogonial incept begins to grow, and soon breaks its way 

 out through the summit of the antheridium, when the formation of the 

 oogonium proper begins to take place. This process seems to occur chiefly at 

 night, and it was only by carrying on continuous observations under the 



