178 Dr. H. Charlton Bastian on Diaioms and the 
More rarely spaces are found densely packed with brownish- 
yellow diatoms only, in different stages of growth and deve- 
lopment, except perhaps for the association of one or two 
minute algoid corpuscles (fig. 4, A, B, C, D) *. 
In regard to the diatoms themselves, these are sometimes 
very small and rudimentary (as in fig. 3, A, and in the upper 
part of D), but at others they are much larger (as in fig. 3, 
B,C, D). These larger sizes are either fairly broad and 
ovoid, like Navicwle, or else narrow and elongated, like 
Nitzschie (fig. 4, C, D). 
In almost all cases, however, the diatoms have the appear- 
ance of being immature; they have ill-developed siliceous 
envelopes and are all quite full of brownish-yellow endo- 
chrome. There are also at times indications that growth and 
multiplication of these immature forms is or has been taking 
place, looking to the way in which they are occasionally 
ranged side by side in short rows in some of the half-empty 
spaces (as in fig. 8, A, and in the upper part of D). 
The substomatal spaces which have been tenanted by the 
Chlorochytrium are characterized, as | have said, by a greatly 
distended and almost circular stoma, and often by having 
their walls stained of a more or less distinct rust-colour. 
Indications of the latter change are to be seen in fig. 2, OC, Df. _ 
It is a fact of much importance that diatoms are never to 
be found in any of the substomatal spaces except in those 
which either actually contain or bear marks of having been 
previously tenanted by Chlorochytrium. 
- Unfortunately I have found it very difficult to photograph 
some of the most remarkable specimens I have met with. 
This has been due to a combination of causes. It has been 
partly owing to the light having to pass through the whole 
thickness of the leaf, partly because of the staining of the 
walls of the spaces, partly because the photograph yields no 
discrimination in shade between the emerald-green colour of 
the alga and the characteristic brownish yellow of the diatom, 
and at other times owing to the diatoms being so densely 
packed within their little subepidermal pockets that their 
individual forms cannot be clearly shown, as in fig. 4, in 
which two of the spaces (C and D) were closely packed with 
* The specimens shgwn in this figure looked much more densely 
packed before the leaves from which they were taken were immersed ii 
elycerine in order to facilitate the taking of the photographs. All the 
other photographs have been taken from leayes immersed in water only, 
except fig. 6, A, which was also taken from a specimen in glycerine. ~ 
} Of course these two characteristics, belonging to different planes, 
van neyer be seen together in the same photograph, 
