Cytology of a new variety of A chly a americana . 153 
and encyst within the sporangium. An oblique section of 
such a sporangium is shown in Fig. 32. I have not been able 
to definitely recognize nuclear divisions, direct or indirect, 
either in the germinating zoospores or in the mycelium, where 
nevertheless they certainly go on. I have still to search for 
them at the base of the main hyphae, where, according to 
Hartog, they take place. An endeavour to follow the fate of 
the nuclei at the apices of the main hyphae has hitherto been 
frustrated by the density of the protoplasm in that region and 
the abundance of the same microsomata which are seen in 
smaller numbers in the zoospores. Many sporangia were 
examined in all stages of development. The nuclei are easily 
traced at this time, and it can be safely concluded that nuclear 
divisions do not take place during the formation of sporangia. 
Development of the gametangia and gametes . Karyokinesis. 
Young oogonia, as observed in stained preparations (Figs. 33, 
34), are seen to possess a very delicate cell-wall which appears 
to be really adherent to the protoplasm. Shrinkage of the 
protoplasm which takes place to a slight extent is accom- 
panied by a shrinkage of the cell-wall, so that one does not 
find even in bad preparations any gap between the cell-wall 
and the protoplasm. The outermost layer stains deeply 
with gentian-violet as if it were made up of microsomata. 
Time has not, however, permitted me to pay so much attention 
to this young cell- wall as the subject deserves. The mature 
cell-wall gives the reactions of cellulose very readily — as easily, 
for example, as those of Spirogyra and Vancheria — and of 
course does not take up gentian-violet. The protoplasm 
exhibits foam-structure, although not so beautifully as in the 
species of Saprolegnia with which I am familiar, and at first 
almost completely fills the oogonium. The nuclei are very 
obvious and are apparently surrounded by a thin layer of 
protoplasm which stains deeply. One is tempted to regard 
this as kinoplasm, more especially as I have seen indications 
within it when well developed, of a fibrous structure. Provi- 
sionally, at any rate, we may regard the protoplasm as 
differentiated into kinoplasm with a fibrous structure and 
