138 NATURAL HISTORY SOCIETY OF DUBLIN. 



Plant monoecious ; oogonia large, barrel-shaped or elliptic, mostly 

 in an uninterrupted terminal series, though occasionally interstitial ; 

 the terminal oogonium the oldest in a series, the oogonia thus showing 

 gradually different degrees of development down to the basal one, which 

 is the youngest ; the lateral male branches (Nebenaste, Pringsheim), 

 with the exception of those fertilizing the lowest oogonium of a series, 

 are not derived either from the principal stem of the plant, or from any 

 neighbouring portion of the general plant, but these are given off from 

 the oogonium itself which is next immediately beneath the oogonium 

 which is fertilized by them, and so on down to the lowest or basal oogo- 

 nium of a series, to which last are given off lateral male branchlets from 

 the original filament or stem immediately thereunder. The tube or 

 cavity of each lateral male branchlet becomes shut off by a septum 

 formed a short distance above its origin, the portion of the contents 

 above the septum being developed into the male element — that portion 

 of the contents below the septum retaining its characters, and being re- 

 turned back into the oogonium, whence it originated, in time to become 

 employed, with the remainder of the contents, in the formation of the 

 oospores. Oospores large, about y-g ^th of an inch in diameter, mostly 

 numerous, but very variable in number — sometimes, though rarely, as 

 few as even one. They occasionally exhibit what appears to be a 

 roundish excentric vacuole. The whole plant large and coarse as com- 

 pared with other described forms in this family. 



If thus, for sake of illustration, we call the upper (mostly terminal) 

 oogonium A, that beneath it B, that beneath the latter C, and so on 

 down, let us suppose, to G ; then oogonium A is fertilized by the la- 

 teral male branchlets emanating from and in direct continuation with 

 B ; the oogonium B is fertilized by the lateral male branchlets, in the 

 same way emanating from C, and so on down to F, which is fertilized 

 by the male branchlets emanating from G ; but G is itself fertilized by 

 the lateral male branchlets emanating from the supporting stem, for G 

 has no oogonium beneath. So, of the whole chain of oogonia, the oospores 

 in each, those of the lowest one excepted, are fertilized by the male ele- 

 ments derived from the branchlets given off by the oogonium immediately 

 below. The terminal oogonium does not, of course, give off any male 

 branchlets ; they would have no duty to do, no function to perform. 

 The contents of the oogonia, which in their turn successively give off 

 lateral male branchlets, do not become formed into oospores until the 

 septa, cutting off the upper portion to become the male element, are 

 duly formed in the branchlets, nor until the granular contents beneath 

 such septa become turned back into the oogonium in time to participate 

 with the remainder of the contents in the formation of the oospores. As 

 in other Saprolegniese, the whole contents of each oogonium become 

 used up to form the oospores, whatever may be their number. The male 

 branchlets seem to penetrate the wall of the oogonium at any accidental 

 point, no special apertures being formed in anticipation, thus unlike cer- 

 tain forms as described by Pringsheim. 



Thus, this species, whilst it agrees with other monooecious forms in 



