140 NATURAL HISTORY SOCIETY OF DUBLIN. 



unskinning from a special mother-cell, that likewise so too are the zoo- 

 spores. If so, this plant would fall under the genus Achlya. 



Another indication pointing to the genus Achlya is as follows : — 



In this new species, not infrequently just under a terminal oogo- 

 nium, the main filament gives off one, or two, or three lateral branches 

 in a kind of proliferous manner, and these are usually of considerably 

 less diameter than that of the supporting stem. These, at first sight, 

 might be supposed to look not unlike what might be intended to become 

 lateral male branches (fig. 5), sufficiently puzzling after one has pre- 

 viously found that the species is a dioecious one ; but when we notice 

 that the oospores are here fully formed, and yet that this lateral branch 

 still retains its contents, and is not in contact with the oogonium, such 

 a mistake is prevented. Such a form as that drawn in fig. 6 at once, 

 however, explains the former case. Here we see the ends of these be- 

 come inflated, densely filled with contents, and shut off as oogonia. In 

 these secondary oogonia I never noticed more than one oospore, although 

 the first- formed oogonia might contain perhaps as many as eight or ten, 

 though ordinarily fewer. 



Now, this proliferous manner of growth is the second circumstance 

 which points to the genus Achlya. In that genus the zoospores, besides 

 being the product of a number of a special mother- cells (not, as in Sa- 

 prolegnia, simple primordial cells formed from the contents of the spo- 

 rangium), the sporangia themselves are, moreover, produced, one or more 

 generations after the first, by being given off laterally at the base of the 

 first (not terminal, as in Saprolegnia, and the new sporangium being 

 pushed up within its now empty predecessor). Now, may not this 

 tendency, seeming inherent in Achlya, to put forth fresh growth late- 

 rally, when about to form new sporangia, be again evinced when about 

 to put forth new oogonia ? May not this kind of innovation, so to speak, 

 be characteristic of the genus Achlya, so far as it is worth? 



The following may serve as a description of this plant : — 



Achlya cornuta, sp. nov. Figs. 2-6. 



Plant dioecious ; oogonia large, mostly terminal, often in an unin- 

 terrupted series, the outer wall drawn out into numerous horn-like 

 extensions of varying and often considerable length, sometimes bifid ; 

 the apex of the terminal one drawn out generally very long, and occa- 

 sionally the supporting filament or stem giving off lateral branches by a 

 kind of proliferous growth, each of which eventually terminates in an 

 oogonium of a similar character, but usually of smaller size ; oospores 

 large, one or several in an oogonium ; mother-cells of spermatozoids'as 

 in Achlya dioica. I have not been able to seeany openings in the wall 

 of the oogonium ; they may doubtless exist, but the densely arranged 

 cornua render the examination with this view very difficult. De Bary 

 himself, in his Aphanomyces stellatus, found the same difficulty from the 

 same cause. ,The uppermost oogonium is the oldest or first formed ; the 

 lowest the youngest or last formed, in the series. 



Here, as is seen, the oogonia occur in a continuous series, several 

 being in succession, separated merely by a septum, or they may be few 



