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ot “ boy ° Structural ent Plysiological Botan 
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ae i and the solid substances and gases contained i in it ina state, Hii 
of solution, there occur also. in the cell various special cell. 
i ae» Contents. To the solid substances of this nature belong pig- i “ a 
-» ments, starch, crystalline formations, aleurone, and “resi 04 4 
oe , or 
to the fluid substances oil, caoutchouc, viscine, and gutta-_ 
percha. The albuminous or proteinaceous substances are’ ys 
sometimes solid, sometimes dissolved. Finally, in the living woo 
cells occur sugar, tannic acid, and inuline, dissolved in water, 
} The most important of these substances is chlorophyll, the source of £29 
_~ the green colour of plants. It is always combined with particles of pro- 
toplasm of definite form, which in consequence appear of a green | F 
colour, and are called chlorophyll-bodies. These occur and are formed 4 
_ only in those cells which possess a cell-wall, never in naked primordial ee i 
Cells. - They are usually lenticular, rarely in the form of bands a 
ie) _ | (asin the Conjugate, Fig. 41), stellate figures, or in undefined flakes. Lag 
Re _ Chemists are not yet agreed as to the chemical composition of chlorophyll ;_ a 
_. but it is probably composed of two independent colouring substances, a — 
golden yellow and a blue-green; it is possible also that iron is an — 
Ly essential constituent of it. The access of light is also an indispensable 
-~ condition for its formation. Plants otherwise green which grow in the 
- dark become bleached or etiolated ; a very small quantity of light is, 
however, sufficient to produce chlorophyll inmany plants that growin the 
shade. The germinating seeds of many Coniferze and the fronds of — - : 
_ ferns afford a striking exception, becoming green even in absolute 
., darkness when.the temperature is sufficiently high. The chlorophyll-. — 
“bodies, which arise from and in the protoplasm, remain subsequently ; 
» imbedded in it, and are especially found in a motionless layer of the : 
_ parietal coating ; rarely, as in Vallisneria spiralis (Fig. 40), in the Cures ai 
ess - rents themselves of the protoplasm. They consist of a colourless pro- 
eat _-toplasmic fundamental substance, in which the green colouring matter ae 
. ~~. is imbedded. They possess no proper membrane, although the outermost 
_» layer is denser, the density decreasing gradually towards the fluidin- 
terior, and affording therefore a comparison with the primordial utricle 
of the protoplasm. In their interior are often found granules of starch, 
which have generally been formed there under the influence of light ; i 
20. while less frequently (in some Muscineze, as Azthoceros and Fissidens 
--  bryoides) they are points of crystallisation around which the mass of oo) 
| chlorophyll has been deposited. The chlorophyll-bodies do not usuaily in- | Poe 
trl crease greatly insize ; but in A/etzeeria furcata (a Hepatica) the diameter : oe : 
has been observed t6 increase from 0°0003 mm. to 0'006 mm. 3 
