LAGEN1DIALES 959 



ulwn, Polysiplwnia urceolata, Pylaiella littoralis, Aleem (1953:11, figs. 

 22-26, pi. 1, figs. 2-3), Sweden. 



Observations on zoospore production in this species (Sparrow, 1934c) 

 showed that the swarmers were fully formed within the sporangium by 

 a process of cleavage, which resembled in its later stages that found 

 within the vesicle of Pythium. The spore initials gradually assumed an 

 individual rocking movement, which became more pronounced as 

 separation and fashioning of the spores proceeded. Around the periph- 

 ery of the spore mass, which at this stage did not completely fill the 

 sporangium, traces of flagellar movement became visible. In later stages 

 the flagella became very apparent, being laterally attached to the 

 shallow-grooved zoospores. These escaped individually, by their own 

 motility, through the discharge tubes. 



Petersenia pollagaster (H. E. Petersen) Sparrow 



Dansk Bot. Ark., 8 (6) :15, pi. 3, figs. I-K. 1934 



(Fig. 76 C, p. 960) 



Pleotrachehts pollagaster H. E. Petersen, Oversigt Kgl. Danske Vidensk. 

 Selskabs. Forhandl., 1905: 462, fig. VI, 1-5. 



Sporangium consisting of a complex of strongly inflated broadly 

 pyriform lobulations, rarely only slightly lobed, large specimens 1 12 by 

 104 [x, small ones 35 by 43 \x, with from one to four cylindrical discharge 

 tubes of variable length (10-100 a); zoospores biflagellate, presum- 

 ably issuing through the discharge tubes; resting spore not (?) ob- 

 served. 



In Ceramium rubrum, H. E. Petersen (loc. cit.), Ceramium sp., 

 Sparrow (loc. cit.), Denmark. 



The characteristic complex of lobulations in well-developed specimens 

 is striking, and cannot be confused with the more open type found in 

 Petersenia lobata. 



Thick-walled resting structures occupying all or part of the lobed 

 thallus have been found by Petersen (see Sparrow, op. cit., pi. 3, figs. I, 

 K). Whether they belong to the fungus or are cysts of extraneous parasitic 

 organisms has not been determined. 



