0LPIDIOP8ID VCKAK 



61 



the parasite as in cases of infection by species of 

 Rozella. The young thallns usually includes a large 

 number of small vacuoles (fig. 8), .'111(1 as it becomes 

 larger these increase in size also and eventually fuse 

 to form i large central vacuole (fig. t). As in the 

 sporangia of Saprolegnia species, this vacuole may 

 extend up through the center of the exit tube and 



often follows ■ spiral path (figs. T. 8). The wall of 



the thallns and sporangia is well defined at matur- 

 ity, but, unlike that of Olpidiopsis and other simi- 

 lar fungi, does not show a marked cellulose reaction 

 when tested with chloro-iodidc of /inc. The exit 

 tuhes may be simple or branched and vary from 1 

 to S per sporangium. They are usually quite long 

 and extend not only beyond the host cell hut through 



the wall of the Spirogyra filament and far beyond its 



surface. 



The central vacuole increases in si/e as the spo- 

 rangia mature until the remainder of the protoplasm 



forms a comparatively thin parietal layer (figs. 4- 

 8). The border of the vacuole becomes quite irregu- 

 lar as broad cleavage furrows are formed (fig. 7) 

 which progress ccutrifugally towards the periphery, 

 .hist before these furrows reach the plasma mem- 

 brane the parietal layer of protoplasm has a char- 

 acteristic scalloped appearance (fig. 8) which corre- 

 sponds to the so-called spore initial stage in the 

 Saprolegniaceae and the "hailing" stage described 

 by Scherffel ('25) for Ectrogella and Aphanomy- 

 copsis. As the cleavage furrows attain the periphery 

 the central vacuole collapses and disappears. The 

 boundaries of tin cleavage segments become quite 



invisible and the protoplasm appears to occupy the 

 entire volume of the sporangium (fig. !)). The latter 

 decreases slightly in si/e at this stage, due possibly 

 to loss of water during the collapse of the central 

 vacuole. This stage is strikingly similar to the so- 

 called homogenous phase of sporogencsis in Olpidi- 

 opsis, "Ectrogella, and the Saprolegniaceae. Very 

 shortly afterwards the fully formed spores become 

 visible i fig. 10) and soon glide out of the sporan- 

 gium as the tip of the exit tube ruptures (fig. 1 1 ). 

 They arc first elliptical in shape and contain two or 

 more conspicuous granules, hut soon round up and 

 encyst and thus form a cluster around the tip of the 

 exit canal (fig. 1 2 ) as in Achlya and species of 



liogenidium, Ectrogella, Aphanomycoptis, etc. 



Within an hour or two the content of the cyst 

 emerges (figs. 1:5—1(5) and is transformed into an 

 oblong bifiagellate isocont zoospore (fig. 17) which 



soon swims away. 



Sexual reproduction in /'. vernalis is heterogam- 



ous. The so-called anthcridiuin and oogonium are 

 quite unequal in size and lie in tin- same gall or swell- 

 ing fig. 18). The anthcridiuin show-, no structural 

 differentiation as a gametangium, and it is accord- 

 ingly questionable whether or not it should be desig- 

 nated as an anthcridiuin in the original sense of the 

 term. The oogonium, on the other hand, contains a 

 large central vacuole and parietal layer of proto- 

 plasm which appear to undergo some degree of dif- 

 ferentiation into ooplasm and periplasm, according 



lo Couch's description. The anthcridiuin forms a fine 

 fusion canal which penetrates the wall of the OOgO 

 nium into the ooplasm (figs. "JO. 21 ). The content of 

 the antheridium thereby flows into the ooplasm and 

 fuses with it. As the zygote matures it forms a fairly 

 thick wall, while most if not .ill of the periplasm 

 gradually disappears (fig. 23). Occasionally two 

 antheridia may fertilize one egg cell (fig. 22) as in 

 species of < )l pidiopsis. 



Nothing is known concerning the origin of the 

 respective gametes in this genus. Whether the thalli 

 which develop into the antheridium and oogonium 

 respectively are derived from zoospores from the 

 same or different zoosporangia is not known. It is 

 accordingly impossible to say at present whether 

 sex differentiation is genotypic or phenotvpic. Fur- 

 thermore, it remains to be seen whether the gametes 

 are multinucleate and their nuclei fuse in pairs or all 

 but one nucleus in each gamete degenerate before 

 karyogamy occurs. 



P. VERNALIS Couch, I.e., figs. 1-27. 



Zoosporangia solitary or up to I in a swelling, 

 spherical or subspherical, 10-.'50 p., sometimes flat- 

 tened when several occur in a gall; exit tubes up to 

 50 p long by 1 p in diameter. Motile zoospores .'5.7- 

 ■i p in diameter. Oogonia spherical or subspherical, 

 1 1-18.5 p. Antheridia hyaline, smooth, slightly flat- 

 tened or spherical, 5 p. Oospore spherical, 9- 15 /i. 

 hyaline, smooth and thick-walled. 



Parasitic in Pythium gracile and P. dictyosporum 

 in North Carolina, U. S. A. 



In connection with the Olpidiopsidaceae brief 

 mention may be made of two unusual and incom- 

 pletely known parasites which Carpenter (TO), and 

 Tehon and Harris ('H) described as forming 

 oospores in somewhat the same manner as 01 pidiop- 

 sis. However, in referring to them here the author 

 does not imply that they should be included in the 

 Olpidiopsidaceae as this family is now recognized, 

 because their thalli are amoeboid and plasmodium- 

 like, and zoospore are not definitely known to occur. 

 The first of these fungi was reported by Carpenter 

 to be associated with chlorotic streak disease of 

 sugar cane in Hawaii. Two developmental phases of 

 the parasite were observed, but the connection be- 

 tween them was not definitely established by Car- 

 penter. The first phase consists of a naked amoeboid 



or plasmodium-like thallns (text-fig. Ai suggestive 

 of that of tin- Plasmodiophorales and Woroninaceae. 



However, no individual movement of the thallns or 

 streaming of the protoplasm was observed, nor docs 



the parasite cause cell stimulation or hypertrophy 



of the host tissues. The second and most conspicuous 

 phase consists of spheres of protoplasm which occur 

 in the parenchyma of the stalk and vary from 5—60/1 

 in diameter and hyaline to gray, brown or black and 



opaque in color. The hyaline spheres. :i 25 ». may 

 have thick walls and resemble hypnospores which, 



according to Carpenter, "appear to be formed by 

 copulation of two units, the content of one sphere 



