CHYTRIDIALES 89 



to the "chromatin cap" described by Wager (1913) in Polyphagus. 

 In addition, a well-defined chromatin reticulum is present and is partic- 

 ularly abundant near the nuclear membrane. The reticulum consists 

 of chromatin granules, net knots, and irregular bodies distributed on 

 a linin framework. The two structures, nucleolus and reticulum, are 

 distinct from each other in appearance, position, and staining proper- 

 ties, a fact which Karling (1937b) believes to argue against the theories 

 of the nucleolar origin of the chromatin. In the spindle organs and the 

 young zoosporangia the nuclei are frequently surrounded by deeply 

 staining granules of unknown origin and nature, strikingly like the 

 "chromidial" material Wager describes in Polyphagus. The position 

 of this material makes it impossible to determine with absolute cer- 

 tainty whether or not centrosomes and astral rays are formed. 



Various prophase stages have been described by Karling (1937b), 

 to whose paper the reader is referred for further details. It is sufficient 

 to say that the chromatin making up the chromosomes in Cladochy- 

 trium replication does not seem to originate from material extruded 

 or discharged from the nucleolus, as it does in certain terrestrial chy- 

 trids (Curtis, 1921 ; Kusano, 1930a, 1930b; and others), but solely from 

 the contracted chromatin reticulum. The reticulum, though oriented 

 on the nucleolus, is distinct and separated from it. There are from six 

 to nine chromosomes, the small size of these structures making precise 

 determination of the number difficult. Some reason exists for believing 

 that the division spindle arises from the linin, although the evidence 

 for this is as yet meager. At the time of its formation the nuclear mem- 

 brane is still very apparent and distinct. The poles of the spindle are 



brane (lower side); F, longitudinal section of developing zoosporangium in 

 which the three visible nuclei are in equatorial-plate stage of division; G-I, 

 sporangia with partly and completely cleaved contents ; in /masses of dense- 

 ly basophilic granules surround nuclei; /, mature resting spore with flattened 

 nucleus lying just beneath wall. K-M. Endochytrium operculatum (de Wild.) 

 Karling: K, young thallus with nucleus in rudiment of endobiotic sporan- 

 gium; L, thallus with two nuclei in sporangial rudiment; what may possibly 

 be extranuclear material is seen at point of attachment of rhizoidal system 

 to sporangial rudiment; M, portion of thallus with multinucleate rudiment 

 of zoosporangium; no nuclei were found in the rhizoids. 

 (A-J, Karling, 1937b; K-M, Hillegas, 1940) 



