Cytology of Polyphagus Euglenae. 191 
spores. Percival (’09) also gives an account of a remarkable nuclear cycle 
in the production of the thin-walled cells of Synchytrium ( Chrysophlyctis ) 
endobioticum. i With the beginning of the reproductive stage, the chromatin 
of the nucleus (primary nucleus) often becomes associated with the linin 
threads. The nucleolus becomes vacuolated and loses its staining power ; 
at the same time the nucleus shrinks and soon disappears entirely, the 
chromatin contained within it being found in the form of very distinct 
“ chromidia 55 scattered through the cytoplasm of the parasite ; round the 
chromidia small vacuoles appear, and nuclei arise at these points.’ No 
primary nucleus was found to undergo recognizable mitotic division, but 
undoubted mitosis occurs in the minute secondary nuclei (p. 443 ). Kusano 
(T2) states that in Olpidium Viciae 1 the nuclei of the sporangium multiply 
during the vegetative or growing phase by an amitotic-like division and 
during the reproductive phase by mitosis . 5 
The very small portion of chromatin which is required for nuclear 
division, the minuteness of the chromosomes, and the prominence of the 
extruded nuclear material render the observation of the various stages 
of nuclear division extremely difficult, and it may well be, especially in 
Synchytrium , where the resting nucleus is so large and the dividing stages 
so small (Stevens, 5 07), that mitotic nuclear divisions have been overlooked. 
In any case, seeing the numerous discrepancies in the descriptions given by 
various observers, and that both in Olpidiopsis , as Barrett (T2) has recently 
shown, and in Polyphagus the nuclear divisions are normally mitotic 
throughout, with well-marked spindles and chromosomes, it is very 
desirable that all these abnormal nuclear divisions should be further 
investigated. 
Kusano’s account of the cytology of the zygote of Olpidium Viciae is 
extremely interesting and presents many points of comparison with my 
own observations on Polyphagus. The two nuclei of the zygote occupy 
a peripheral position, usually opposite each other. After it has attained 
its maximum growth chromatin is extruded into the cytoplasm, partly 
by a process of budding of each nucleus and partly by the extrusion of 
nucleoli. This chromatin accumulates in the central region of the zygote 
in the form of a chromidial network, and is deeply stainable. At a later 
stage the stainable substance occupies the central portion of the zygote as 
large globules which look like oil-drops. At a still later stage a dissolution 
of the stainable substance takes place and the cytoplasm appears homo- 
geneously granular, being hardly stainable. Fusion of the nuclei does not 
take place until shortly before germination. Kusano mentions that cyto- 
logically the Fungus shows a certain resemblance to the Protozoa or the 
Plasmidiophoraceae. 
