CHYTRIDIALES 65 



monocentric epibiotic phase of certain species of Physoderma (Biisgen, 

 1887; Clinton, 1902; Sparrow, 1934a, 1946). 



Structure arid behavior of the zoospore. — The zoospore of the chytrid 

 (see also "Zoospore," p. 7; Fig. 1 A-B, p. 8) is a highly characteris- 

 tic structure, its internal organization being so remarkably uniform 

 throughout the group that an experienced observer of these fungi can 

 recognize it even when it is free-swimming among aquatic debris. The 

 body, which appears to have no well-defined wall, is ordinarily spheri- 

 cal or somewhat ovoid, usually with the broader end posterior. In 

 certain forms, however, it is obovoid {Rhizophlyctis mastigotrichis), 

 cylindrical with rounded ends (Polyphagus euglenae), or rodlike (Rhi- 

 zophydium goniosporum). The plasma of the body is generally some- 

 what lustrous and is homogeneous or bears a few minute refractive 

 granules or contains a globule. A nucleus and a nuclear cap may some- 

 times be detected, but as a rule these are invisible in the living zoospore. 

 The most conspicuous element in the body is the large refractive glob- 

 ule, which may lie near or at the center (centric) or, more often, 

 near the periphery (eccentric). Occasionally, as in Rhizophlyctis masti- 

 gotrichis, it is basal. The globule is extremely minute in some species, 

 but in others it occupies approximately two thirds of the whole body. 

 A few exceptions to this characteristic internal organization are found. 

 Thus in Olpidium vampyrellae (Scherffel, 1926a) no globule is formed, 

 whereas in Cladochytrium granulatum, for example, zoospores with 

 several globules are produced. In general the type of organization of 

 the zoospore remains relatively constant in a given species. * 



Various conjectures have been made in the past as to the nature 

 and function of the globule in the zoospore of the chytrid. Early in- 

 vestigators supposed it to be the nucleus, but, probably because of 

 its fatty appearance, soon abandoned this view. Indeed, A. Braun 

 (1856a) himself suggested that it might be oleaginous, and it has since 

 been most commonly referred to as an "oil globule/' Microchemical 

 tests by Karling (1937b) indicate that the globule of the zoospore of 

 Cladochytrium replica turn is of a more complex nature. Hillegas (1940) 

 has reported similar findings in Endochytrium operculatum and Anti- 

 kajian (1949) reports it in Asterophlyctis sarcoptoides to be of fat and 

 some other accessory substance. 

 1 See Koch (1958) for a detailed study of the chytrid zoospore by light microscopy. 



