DUDRESNYA. 121 



pogonium is developed from the end cell of a short branch (Fig. 47, 

 A), whose remaining cells give rise to numerous side branches (Fig. 

 47, B). The end cells of these side branches may become auxiliary 

 cells. The trichogyne is unusually long, showing spiral-like turns 

 either at its middle or nearer the base. The nucleus lies in the ventral 

 part of the young carpogonium. Later it passes up into the tricho- 

 gyne, and when the carpogonium is ready for fecundation, the nucleus 

 is to be found in the coiled region of the trichogyne (Fig. 47, C). The 

 spermatium applies itself to the tip of the trichogyne, which projects 

 slightly beyond the general surface of the thallus. The cell-walls at 

 the point of contact are dissolved, the sperm-nucleus passes down into 

 the trichogyne and fuses with the egg-nucleus in a manner described 

 by Wille ('94) for Nemalion. 



Oltmanns did not observe the actual fusion of the sexual nuclei in 

 Dudresnya, but in repeated instances two nuclei were seen lying 

 tolerably near each other in the trichogyne, and at a later stage a 

 single nucleus was found in the ventral part of the carpogonium, 

 which he regarded as the fusion-nucleus. The union was observed, 

 however, in Dasya elegans, and personally Oltmanns believes the 

 fusion in Dudresnya to be too probable to justify an exhaustive study. 

 It may be remarked that in general this is by no means a safe principle 

 to follow. 



After fecundation the base of the carpogonium (or shall we say the 

 fecundated egg-cell) segments into cells which increase in size and 

 begin to grow into sporogenous filaments. In Dudresnya purpu- 

 r if era two or three of such filaments arise from the carpogonium, 

 one on either side, with sometimes a third between them (Fig. 47, 

 D, sf). The sporogenous filaments, which soon become segmented 

 into cells by transverse walls, grow downward among the lateral 

 branches of the carpogonial branch and fuse with some of the end 

 cells of these branches, which have become auxiliary cells (Fig. 47, E, 

 az) . Certain cells of the carpogonial branch may function also as 

 auxiliary cells. The auxiliary cells are distinguished by their form and 

 denser protoplasmic contents. Usually only one cell of a sporogenous 

 filament unites with an auxiliary cell or cells. 



The filaments continue their growth in length, fusing with other 

 auxiliary cells which may be borne upon other and widely separated 

 vegetative branches (Fig. 49). The fusion of any auxiliary cell with 

 that of a sporogenous filament represents only a cytoplasmic fusion 

 and not a sexual act. This process with the immediate subsequent 

 changes is briefly as follows : As soon as the cell-walls at the point 



