906 



AQUATIC PHYCOMYCETES 



thallus in the Olpidiopsidaceae is free in the host cell it may be carried, 

 perhaps at first by its own action (Diehl, 1935), but more likely by the 

 cytoplasmic currents of the host (Diehl, op. cit.\ McLarty, 1941a), for 

 varying distances away from the original point of infection (Fig. 73 D-H, 

 below). Often it tends to develop in the more distal regions of the hypha, 

 though in other instances it remains intercalary. Wherever the thallus 

 develops, a marked hypertrophy of the host occurs (Fig. 73 I). The 

 stimulation to swell, or to produce lateral outgrowths, may possibly be 



1 



B 



:>00 O :. 



D 



_>-'•■ 



1 



H 



Fig. 73. Olpidiopsis achlyae McLarty on Achlya 



A. Free-swimming zoospore. B-C. Two quiescent zoospores showing changes 

 in shape of body. D. Zoospore quiescent on outer surface of wall of host hypha, 

 other boundary of which is not shown. E. Encysted spore, which has now 

 produced penetration tube that has pierced host wall. F. Encysted parasite af- 

 ter contents have been discharged into host. G. Very young thallus of parasite 

 being swept away (to left) from tip of penetration tube by streaming host 

 protoplasm. H. Two young thalli of parasite suspended in peripheral cytoplas- 

 mic layer of host. /. Two more mature thalli which have assumed a central 

 position in now distinctly swollen tip of host filament. 

 (McLarty, 1941a) 



