84 THE LOWER FUNGI—PHYCOMYCETES 



metes (Fig. 18, k, m). In the accounts of early workers on the 

 Synchytriaceae so many references to the observation of giant 

 bicihate swarmspores occur that a sexual fusion of ciliate cells 

 has long been suspected. The demonstration of its occurrence 

 in this species makes logical the assumption that the resting 

 spores of other species are also truly sexual in nature. In 

 this connection the discussion of planogamic copulation given 

 above (p. 81) should be read. In this species, as in S. taraxaci 

 discussed above, both summer sori and resting spores are formed. 

 The resting spore in germination produces swarmspores directly. 

 These infect the host and produce thalli which at maturity func- 

 tion as prosori. The prosorus is provided with a thick orange 

 exospore and a thin hyaline endospore. At first it is uninucleate 

 (Fig. 18, a-c). The cytoplasm and nucleus pass out into a vesicle 

 consisting of the extruded endospore, and in this vesicle nuclear 

 division occurs, approximately a dozen nuclei being formed 

 before the sporangia are delimited. The sporangial walls are 

 formed simultaneously and independent of the nuclei, about 

 four to nine sporangia composing the sorus. The extrusion of the 

 endospore occurs while the fungus still lies in the host cell, and 

 the exospore may be flattened out at one side by the pressure 

 exerted by the protoplast, and at maturity be relatively incon- 

 spicuous. Nuclear divisions continue in the sporangia until two 

 hundred to three hundred nuclei are formed in each. The 

 enlarging sporangia exert sufficient pressure to finally rupture the 

 soral membrane and the wall of the host cell, and are thus set free. 

 Then one or two hyaline papillae are formed on each sporangium, 

 and, at the rupture of one of these, numerous uninucleate motile 

 cells escape. Some of these motile cells function as swarmspores 

 and after infecting the host develop into other prosori. Some 

 of them function as gametes and fuse in pairs, the resulting 

 zygote penetrating into the host and developing there into a 

 resting sporangium. It is probable that the two gametes which 

 fuse originate in different sporangia, though the point is difficult 

 to demonstrate. Their nuclei fuse in the zygote before infection 

 occurs. The mature resting spore swells by the imbibition of 

 water and bursts, freeing swarmspores directly. Other species 

 belonging in the subgenus Mesochytrium are S. succisiae de Bary 

 & Woronin on Succisa, S. cellulare Davis (1924: 287) on 

 Lycopus, and S. stellariae Fuckel on Stellaria. In the subgenera 

 Eusynchytrium and Mesochytrium few data are available concern- 



