MEMBRANE. 
7 
Membrane in its earliest stages is thin, transparent, 
and structureless, as shown in the outer membrane of 
the seed of a Gourd , Fig. Lb, or at a, which repre- 
sents cells obtained from the young dower-stem of a 
Leek. It is generally colourless, or has a greenish- 
white hue ; in some cases, however, as in ferns, it is 
brown. The beautiful and varied colours of the corolbe 
of flowers do not depend upon the membrane com- 
FIG. l. 
A B 
a, cells from the flower-stem of a Leek ; a, cell- wall ; b , nucleus, b, epi- 
dermis of the seed of the gourd, composed of cells. 
posing the cells, but on the colouring matters which, 
chiefly in a fluid state, are contained in their interior. 
Membrane is also, at the stage at which I am describing 
it, entirely free from visible pores, although fluids readily 
pass through it by endosmose and exosmose ; and, 
notwithstanding many cells and vessels, hereafter to 
be described, have their walls studded with dots and 
apparent foramina, the membrane is always present, 
but, in most instances, so excessively thin, that it 
