46 
ORGANOGRAPHY. 
BOOK I. 
distinguished by presenting itself in irregular granular bodies 
without any internal structure, and becomes brownish yellow 
or brown when tested with tincture of iodine. This may be 
called mucus, and appears to be what the Cytoblast and its 
spherule are composed of. When starch is about to assume a 
new organization, it converts itself, in some manner unknown 
to chemists, into sugar or gum. 
Sugar makes its appearance as a transparent fluid, which 
seems as clear as water, is not rendered turbid by alcohol, 
and is coloured by tincture of iodine, according to the greater 
or less degree of dilution of that agent. 
Gum appears as a yellowish, more consistent, less trans- 
parent fluid, which, with tincture of iodine, coagulates into 
a pale yellow ungranulated colour. When vegetation has 
advanced to that point that gum is the latest immediate pro- 
duct, there appears in it a great many minute molecules, 
which are generally so small as to resemble dark points ; at 
that time the fluid becomes a darker yellow upon the appli- 
cation of iodine. But the molecules, if they are large 
enough to show their colour, become dark-brown yellow. It 
is this mass, so transparent that it can hardly be seen till it 
is coloured, in which, in all cases, organization commences, 
and from which the youngest structure is constituted. It 
may be called Vegetable Jelly, and is probably nearly the 
same as Pecten, the base of Gum Tragacanth, and many 
other kinds of vegetable mucus. It is this jelly, which, by 
a further chemical attraction, becomes the membrane of cells, 
and is afterwards the material by which it is thickened. 
2. Chlorophyll or Chromule. — To this is referred all the 
kinds of coloured granules which occupy the interior of 
vegetable tissue. They have a spheroidal, irregular figure, 
are often rather angular, consist of a semi-fluid gelatinous 
substance not contained in a sac, and which seems to be a 
coagulum of the fluid contents of the cells. The colour of 
plants, especially the green colour, is produced by the pre- 
sence of chlorophyll, which may be considered a vital secretion. 
It will be mentioned more particularly in Book II., in the 
chapter upon colour. 
