54 AQUATIC PHYCOMYCETES 



ridales. by some accessory substance. (SeeNabel [1939] for a discussion 

 of the occurrence of chitin and cellulose in the lower fungi.) 



In the active vegetative stage the cytoplasm of the chytrid presents 

 a typically lustrous gleaming aspect, and is further characterized by 

 the presence within it of vacuoles, refractive, probably fatty, masses, 

 and minute globules. As the thallus matures changes occur in the cyto- 

 plasm. In that of Obeliilium mucronatum, for example, the globule of 

 the zoospore persists in the homogeneous protoplasm for a time after 

 germination. Eventually it disintegrates, conspicuous vacuoles appear, 

 and the protoplasm of the reproductive rudiment assumes a watery 

 aspect. With the enlargement of the thallus there follows a stage in 

 which the protoplasm is densely and uniformly granular. Minute re- 

 fractive droplets, sometimes in rings, then make their appearance and, 

 accompanied by a gradual ''clearing" of the whole protoplasm, coalesce 

 to form regularly spaced conspicuous refractive globules. During the 

 densely granular stage the delicate rhizoids are completely drained 

 of their contents and septa are laid down cutting off the sterile and 

 fertile parts of the thallus. Little can be observed of the contents of 

 the rhizoids other than vacuoles in a finely granular matrix and occa- 

 sional fatty globules. 



In most chytrids the cytoplasm and its globules are colorless. In 

 Polypliagus euglenae, Siphonaria variabilis, Rhizoclosmatium aurantia- 

 cum, Cladochytrium replication, Zygochytrium, and others, however, 

 in the later stages of maturation, the protoplasm becomes shot through 

 with minute golden or reddish-orange globules. It is these droplets 

 which eventually fuse at maturity to form the regularly spaced colored 

 globules, one in each zoospore. Though in the species cited the pig- 

 mented material is found in the globules of the zoospores, in certain 

 others it is retained in the cytoplasm. Sorokin (1874a) found the blue 

 coloration of the cytoplasm of Tetrachytrium to be homogeneously 

 dispersed throughout, even after the zoospores were formed. On the 

 other hand. Zopf (1892) noted that the brilliant orange hue of the 

 vegetative stage of Pleotrachelus fulgens was only temporary, for at 

 maturity the zoospores were colorless. He was probably correct in 

 stating that this coloration was due to the ingested carotene material 

 of the host (Pilobolus). 



