KING: CYTOLOGY OF ARAIOSPORA PULCHRA. 
227 
have been carefully investigated, Pythium and the Peronosporineae , 
form a vacuolate, periplasmic cell about the oosphere but in these 
plants it apparently is not cut up into cells. The great number of 
cell divisions taking place in the oogonium of Araiospora together 
with its unusually coarsely vacuolate cytoplasm, suggested that it 
might be favorable for the study of the origin of the plasma mem¬ 
branes. After considerable investigation, there is still some doubt 
as to whether these membranes are laid down separately or by the 
splitting of a previously formed, single one. There is more evidence 
to suggest that they are formed in the first mentioned way; for 
example, on the upper side of figure 15 (plate 12) in the region 
where these membranes are known to arise, two almost parallel, 
slightly differentiated strands are separated by a row of small alveo¬ 
lae. The writer is inclined to the view that as these strands 
become better differentiated they are finally separated by the 
fusion of the intervening alveolae. Cell walls are now laid down 
between adjacent peripheral cells as well as between the latter 
and the oosphere. These walls are fully developed in figure 
18 (plate 18). 
From the manner in which the peripheral cells arise, it is readily 
seen that each contains at the outset only a small amount of proto¬ 
plasm which in each case separates the enclosed vacuole from the 
surrounding cell wall. Within each of these cells there is certainly, 
in many cases, at least one nucleus and often more. In the latter 
case they are smaller and almost invariably found in groups suggest¬ 
ing that division may have taken place in the peripheral cells (pi. 
13, fig. 18). There are over the surface of an average oogonium, 
probably from sixty to seventy of these peripheral cells. Since 
each builds a wall over at least a portion of its surface, it is evident, 
if the nucleus controls metabolic activity, that there must be at 
least one present in each cell. As a matter of fact two nuclei are 
frequently found in young peripheral cells; this gives additional 
evidence that there has been a division of the thirty-five or more 
nuclei that originally entered the oogonium. It may be mentioned 
at this time, also, that there is a probable homology between the 
walls that are built by the peripheral cells of Araiospora and the 
characteristic reticulated markings found on the surface of the 
oospores of Rhipidium (Tliaxter, ’96) and certain P eronosporineae 
(Berlese, '97). Certainly the formation of the peripheral vacuoles 
