110 
HISTOLOGY OF VEGETABLES. 
interior of the cell, or be deficient in certain parts, when 
pits or pores result, or it may occur in a spiral form, 
the general direction of which is from right to left. 
I next called your attention to the various forms 
under which cells are found in plants, and explained, that 
in the young state and when unaltered by pressure, they 
are of a spherical figure, which becomes modified in 
process of growth into dodecahedrons, cubes, paral- 
lelograms, prisms, &c. &c., and even into fibres. I 
then passed on to the consideration of the contents of 
these cells, and gave examples of various colouring 
matters in a fluid state, which produce all the varied 
hues of the corollse of flowers. I next noticed one of the 
most common of cell-contents, and the most useful to man- 
kind, viz. : starch, which possesses definite and peculiar 
characters in different plants, and consists of granules of 
a more or less oval figure, composed of an outer mem- 
brane exhibiting a central spot or hilum and concentric 
lines, within w T hich the amylaceous or starchy material 
is contained. I pointed out the relative sizes of the 
starch granules in Rice , Potato , and Tons les mois, and 
drew attention to the peculiar club-shaped bodies found 
in the milky juice of the Euphorbiacece. 
Chlorophylle, a substance of a starchy nature, and 
the material that gives the green colour to all plants 
growing in the light, was next considered ; striking 
examples of it occur in the Chara and Vallisneria , in 
both of which plants the granules may be seen in active 
circulation within the vegetable cell. Other cell-con- 
