64 



THE SIMPLE HOLOCARPIC BIFLAGELLATE PHYCOMYCETES 



sporangia as in Sirolpidium. This striking similarity 

 becomes evident when figures 13 and 14\ Plate 16, 

 of S. Bryopsidis are compared with figures 4 and 5, 

 Plate 17, of S. (Pontisma) lagenidioides. The tend- 

 ency to greater or less fragmentation may well be a 

 specific instead of a generic difference. Sparrow 

 further reported that the zoospores are slightly dif- 

 ferent in the two genera, but his descriptions and fig- 

 ures of the positions of flagella are somewhat indefi- 

 nite and unclear. Here also the differences may be 

 only specific. 



Infection of the host and the early developmental 

 stages are not well known in all species, and the fol- 

 lowing account of these processes is based largely on 

 S. Bryopsidis. As in Eurychasma and E.cirogella, the 

 zoospore comes to rest on the host cell, encysts, and 

 soon develops a germ tube which penetrates the host 

 wall. Its content flows into the host cell, while the 

 spore case and penetration tube are left behind and 

 remain attached for some time after germination. Ac- 

 cording to de Bruyne, the young thallus (figs. 6-8, 

 plate 16) very early develops a wall or membrane 

 which thickens with age and shows a weak cellulose 

 reaction when tested. The thallus may develop into 

 an oval, pyriform, ellipsoidal sporangium or elon- 

 gate into a tubular filament, become septate, and 

 then fragment into a number of segments (figs. 11, 

 12, 13, plate 16). These fragments then develop into 

 olpidioid sporangia of various sizes and shapes (figs. 

 IK 15. plate 16) and form one simple or branched 

 exit tube of variable length. The latter may curve 

 about in the host cell or penetrate the latter's wall 

 and project for a long distance on the outside (fig. 



I. plate 16). The same type of development appar- 

 ently occurs in >S'. lagenidioides with the exception 

 that the segments of the irregularly elongate thalli 

 rarely separate. 



The protoplasm of the thalli and incipient zoo- 

 sporangia is glistening and refringent in appear- 

 ance with numerous suspended globules ( figs. 6-9, 

 plate 16; figs. -1, 5, plate 17). When young the zoo- 

 sporangia contain numerous small vacuoles (figs. 



II. 15, plate 16; fig. 6, plate 17) which apparently 

 flow together at maturity and form a large central 

 one as in Olpidiopsis, Pythiella, and other similar 

 genera. So far nothing is known about cytokinesis, 

 but it is apparently accomplished by centrifugal 

 cleavage furrows which progress from the border of 

 the central vacuole to the periphery and thereby de- 

 limit uninucleate spore rudiments. The zoospores 

 complete their development in the sporangium (fig. 

 1, plate 16) and become very active and motile be- 

 fore the tip of the exit tube deliquesces. According 

 to Sparrow they swim directly away after emerg- 

 ing, but de Bruyne reported that in .S'. Bryopsidis 

 they may pause for a few moments at the tip of the 

 exit tube and become amoeboid. He also figured them 

 as anteriorly uniflagellate and occasionally under- 

 going division (figs, i, 5, plate 16). Petersen re- 

 ported them to be uni- and biflagellate, but accord- 

 ing to Sparrow they possess two flagella of equal 

 length inserted at or near the anterior end (fig. 2. 



plate 16). His figures of fixed and stained zoospores 

 (fig. 3, plate 9), however, show the two flagella lat- 

 erally attached. In S. lagenidioides, he reported 

 that the two flagella appear to arise from the con- 

 cave central region (fig. 2, plate 17), while in some 

 zoospores they seem to be attached to the narrow 

 anterior end (fig. 3. plate 17). 



The presence of resting spores has not been dem- 

 onstrated with certainty in Sirolpidium. In S. Bry- 

 opsidis, de Bruyne reported that the contents of oval 

 and globular thalli may contract and become in- 

 vested with a thick hyaline smooth wall (fig. 18, 

 plate 16), and, according to Sparrow ('34) Peter- 

 sen also observed occasional thick-walled spores 

 which he believed relate to this species. So far none 

 have been found in S. lagenidioides. 



Unlike Eurychasma and Eurychasmidium, Sirol- 

 pidium does not cause enlargement of the infected 

 cells. Furthermore, neither they nor adjacent 

 healthy ones are stimulated to divide. The effects of 

 the fungus are local and confined to infected cells. 

 In the case of Bryopsis infected with S. Bryopsidis, 

 heavily parasitized plants may be recognized by the 

 presence of blackened areas along the fronds, which 

 are apparently areas in which the cells have been 

 killed. As the parasite increases in size the plastids 

 turn greenish-brown in color and eventually become 

 clumped together with the remainder of the degen- 

 erating protoplasm, according to de Bruyne's fig- 

 ures. Sirolpidium lagenidioides, on the other hand, 

 appears to be a weak parasite or saprophyte on 

 Ceramium and is capable of growth and develop- 

 ment under conditions unfavorable to its host. 



plate 16 

 Sirolpidium Bryopsidis 



(Figs. 1, 4-9, 18 after de Bruyne, '90; fig. 11 after Peter- 

 sen, "05; figs 2, 3, 10, 12-17 after Sparrow. "34.) 



Fig. 1. Tip of Bryopsis plumosa branch with four zoo- 

 sporangia containing zoospores; the exit tube of one spo- 

 rangium is entirely intramatrical. 



Fig. 3. Free hand drawing and interpretation of the 

 zoospore showing tapering anterior end with a refractive 

 globule and the ventral groove from which flagella ap- 

 parently arise. 



Fig. 3. Zoospore killed in osmie acid fumes. 



Figs. 4, 5. Division of zoospores. 



Figs. 6-8. Young thalli with numerous refractive glob- 

 ules. 



Fig. 9. Elongate and branched thalli. 



Fig. 10. Young stage of fragmenting thallus. 



Fig. 11. Early stage of thallus division. 



Fig. 1-'. Elongate thallus fragmenting; traces of old 

 thallus wall connecting the fragments. 



Fig. 13. Elongate fragmented thallus. 



Fig. 14. Fragments becoming transformed into zoo- 

 sporangia. 



Fig. 15. Incipient, vacuolate, lobed zoosporangiuni with 

 long exit tube. 



Fig. 16. Emergence of zoospores from olpidioid spo- 

 rangia. 



Fig. 17. Tip of Bryopsis filament with numerous olpi- 

 dioid sporangia. 



