Fission-products of a Parasitic Alga. 185 
very minute apertures which they themselves form; but in 
this species of duckweed there are no widely dilated stomata 
through which in earlier or in later stages, should they 
attempt it, diatoms would be free to enter. 
Another point is also of much importance, and that is the 
frequency with which diatoms may be seen around the peri- 
phery of spaces still densely crowded with Chlorochytrium- 
products which have not yet begun to emerge. These 
diatoms therefore make their appearance within closed cavities 
and often in regions far removed from the original point of 
entry of the active algoid spore. No infection hypothesis, 
even backed by a further hypothesis of chemotaxis, is, I 
submit, capable of explaining the presence of these diatoms. 
They are evidently formed where they are found by a trans- 
formation of the algoid cells, and different stages of the 
process may often be clearly recognized, the spherical cells, 
as I have said, becoming elongated and changing from a 
bright green to a brownish-yellow colour as they take on the 
forms of the diatoms *. 
EXPLANATION OF PLATE XV, 
All the components of figs. 1-3 have been photographed at a magnifi- 
cation of 250 diameters except fig. 2, B; this, as well as all the compo- 
nents of figs. 4, 5, 6, have been taken at a magnification of 375 diameters. 
Fig.1. A, shows two stomata of Lemna gibba which have been pene- 
trated by spores of Chlorochytrium Knyanum; in the lower one 
the spore has divided. B, a group of Chlorochytrium cells within 
a substomatal space. C, another group (older) in which the 
cells are more closely pressed together. D, astill older patch of 
Chlorochytrium that has begun to yield spores, some of which 
have passed out and are lodged between the spherical cells 
situated underneath the epidermis. 
Fig. 2, A, several contiguous patches of Chlorochytrium, showing fission- 
products varying much in size. B,asingle large Chlorochytrium 
cell which is full of spores. C, a partially empty sub-stomatal 
space containing fission-products of medium size. D, a similar 
partly empty space containing diatoms of medium size. The 
wall of the space was distinctly more brown in D than in C. 
Fig. 3. A, a mixture of fission-products and of diatoms of different sizes 
within a space. 8B, another space containing rather larger 
fission-products mixed with rather large diatoms. C, like the 
last, only with a much larger number of diatoms than of fission- 
products. D, a space containing larger diatoms still, together 
with some very minute ones in an upper extension of the space. 
The diatoms shown in this figure are probably different kinds 
of Navicule. 
* In my ‘Studies in Heterogenesis,’ Part iii. Sec. xiii. p. 181, I have 
described and illustrated the origin of diatoms from other algoid cells which 
are often to be found on the surface and in the substomatal spaces of the 
different species of duckweed, 
