ARE THE DESMIDS AND DIATOMS SIMPLE CELLS? 
133 
Advancing a step higher, but still confining myself to struc- 
tures which avowedly come within the definition of 64 simple 
cells,” we find in Glosterium , one of the Desmidiacese, that at 
the period when the frond is just matured, the cavity bounded 
by the cellulose wall is completely filled with protoplasm ; and, 
so long as the frond is uninjured, this protoplasm presents itself 
in two somewhat different states ; the one, which constitutes the 
true endochrome and the hulk of the cell contents, being of an 
emerald-green colour and minutely granular ; * the other amor- 
phous, almost if not wholly devoid of colour, and constituting 
(according to my interpretation of the appearances) a thin well- 
defined but free layer between the true cell that surrounds the 
coloured endochrome and the immediate inner surface of the 
cellulose or mere protective covering. It is at this point that 
my interpretation of cell structure (so far as these lowest plant 
types are concerned) diverges materially from that which has been 
arrived at by other observers. For whilst it has been customary 
to regard the surface film of colourless protoplasm as a mem- 
brane, or guasi-membrane, and to assign it a position, in the 
normal condition of the organism, immediately in contact with 
the inner surface of the cellulose wall, I am now prepared to 
show that, in the Desmidiacese, the only portion of the general 
protoplasmic substance that can with truth be said to constitute 
either a membranous or quas ^-membranous investing film does 
not form part and parcel of the colourless protoplasm, but of 
the coloured protoplasm or endochrome, by which it is secreted in 
the shape of a closely investing boundary wall. And, reasoning 
on this fact as distinctly noticeable in Closterium , and other 
elongate species of the Desmidiaceae, and on actual observation as 
regards the changes that take place from time to time within the 
so-formed cell, it seems legitimate to assume that the colourless 
protoplasm is solely concerned in the processes of development 
that go on exteriorly to its surface, whilst the true endochrome 
is solely concerned in the inauguration and establishment of the 
processes connected with the reproduction and multiplication 
of the organism which take place within it. 
It is true that some writers who have given a great deal of 
close attention to the subject, altogether deny the existence of 
any kind of investing membranous structure within the cellu- 
lose wall ; and describe the portion of the colourless protoplasm, 
to which the name of “ primordial utricle ” has been applied, 
as a “ mere pellicle produced by coagulation of the surface of 
the protoplasm, just as a c skin ’ forms over size or other similar 
* It is almost superfluous to observe that I abstain from entering into any 
description of various other minute portions of the structure, solely because 
these are in nowise connected with the present inquiry. 
