PHYTOGENESIS. 237 
In the further progress of organization (in which process the 
gum is always the last, immediately preceding fluid), a quantity 
of exceedingly minute granules appear in it, most of which, 
on account of their minuteness, look like mere black points. 
Iodine then seems to colour the fluid a somewhat darker 
yellow. The granules, however, when their size is sufficiently 
large to render their colour perceptible, become of a dark 
browuish-yellow under its influence. 
It is in this mass that organization always takes place, and 
the youngest structures are composed of another distinct, per- 
fectly transparent substance, which presents an homogeneous 
colourless mass when subjected to pressure; when dried it 
imbibes water and swells; it is not at all affected by tincture 
of iodine, nor does it ever imbibe it; after pressure it appears 
as colourless as before, and is so completely transparent as to 
be altogether invisible when not surrounded by coloured or 
opaque bodies. This substance frequently occurs in plants (for 
example, in great quantity, together with a little starch, in 
peculiar large cells in the tubers of Orchis) ; for brevity’s sake 
I shall call it vegetable gelatine; and am inclined to class 
under this head, as mere slight modifications, pectine, the basis 
of gum tragacanth, and many of those substances which are 
usually enumerated under the term vegetable mucus. 
It is this gelatine which is ultimately converted by new 
chemical changes into the actual cellular membrane, or struc- 
tures which consist of it in a thickened state, and into the 
material of vegetable fibre. 
I now pass on to our subject itself. There are two situa- 
tions in the plant in which the formation of new organization 
may be observed most easily and clearly, in consequence of 
there being cavities closed by a simple membrane, viz. in the 
large cell, which subsequently contains the albumen of the 
seed, the embryonal sac, and in the extremity of the pollen- 
tube, from which the embryo itself is developed. The em- 
bryonal sac never contains starch originally, but probably, in 
most instances, the saccharine solution (which gives the sweet 
taste to unripe pod-fruits and the Cerealia), or gum. 
The pollen, on the contrary, always contains starch, or the 
above-mentioned granulous mucus representing it, as an essen- 
tial constituent part. The so-called vegetable spermatozoa 
