400 AQUATIC PHYCOMYCETES 



Rhizosiphon anabaenae (Rodhe et Skuja) Canter x 



Ann. Bot. London (N.S.), 15: 141, figs. 4, 6-8, pi. 9, B-D, pi. 10. 1951 



(Fig. 11 L, p. 110) 



Phlyctidium anabaenae Rodhe and Skuja, Symbolae Botanicae Upsaliensis, 



9 (3): 379, pi. 39, figs. 9-12. 1948. 

 Phlyctidium anabaenae Fott, Vestnik Kralovske Ceske Spolecnosti Nauk. 



Tfida Mat.-Prirodovedecka Rocnik, 1950 (4): 4, figs. 7-14. 1951. 



"Endobiotic prosporangium spherical, 5-11 \i in diameter, arising 

 as a swelling from the tip of the germ-tube of the zoospore. Sporangium 

 pear- (8—13 [jl high by 4.6-8.5 [jl in diameter), sack-, or retort-shaped 

 (8—14 jjl high by 18-27 \x long) with a mucilaginous dehiscence papilla. 

 Resting-spore formation pieceded by fusion of isogamous gametes, one 

 of which has previously come to rest and? germinated. Resting spore 

 endobiotic, spherical to subspherical, 10-17 \i in diameter, with a 

 thick, smooth, yellowish undulate wall; content consisting of several 

 large globules" (Canter, he. cit.). 



Parasitic and causing hypertrophy of Anabaena in plankton, Rodhe 

 and Skuja (be. cit.), Sweden; Anabaena affinis var. intermedia, A. 

 spiroides, Canter (1953: 287), Great Britain. 



In this species infection is confined to a single cell and no tubular 

 outgrowths of the prosporangium are formed. Although this is not 

 clear from Canter's description, the sporangium is transversely placed 

 on the host cell, and is somewhat campylotropous or saddle-shaped, 

 with a well-developed, lateral tubular part terminated by a discharge 

 papilla. 



Canter (1951), who studied this species from material furnished by 

 Rodhe, noted that "Whereas the zoospore in R. crassum encysts on, 

 or just within, the mucilage of the algal filament and produces a fine 

 thread to the vegetative cell, the zoospore of Phlyctidium (Rhizosiphon) 

 anabaenae always settles on a heterocyst. It then produces a short, 

 lateral thread to an adjacent host cell." She concluded, therefore, that 

 it was fairly certain that resting-spore formation was preceded by sexual 

 reproduction. In this process two isogamous gametes adhere and encyst 

 and the contents of both pass through a tube, formed by the receptive 

 thallus, into the host cell where the resting spore is formed. 



1 See Paterson (Mycologia, 50:94. 1958). 



