28 CONTENTS OF CELLS.—CHLOROPHYLL. 
of the cell. In the early stages of the cell’s life, as we have 
already seen (page 22), before any vacuoles have appeared, the 
cell-sap as a substance distinct from the protoplasm does not 
occur, but is diffused generally through it and the cell-wall, 
and it is only as the cell enlarges that it first appears in vacuoles 
in the protoplasm (fig. 38 and 39, s’, s’), and which by ulti- 
mately coalescing form a single cavity filled with sap, s, s. Be- 
sides containing substances which are necessary to the life of 
the cell, it contains also many things which have been thrown 
out from the protoplasm as no longer serviceable. Of this 
nature are the crystals of calcium carbonate and calcium oxalate; 
hence the cell-sap may be regarded from one point of view as 
the food upon which the protoplasm lives, and from another 
point of view as the reservoir into which it pours out certain of 
its waste products. 
Beside the fluid cell-sap, there are other important cell-con- 
tents, some of which, such as chlorophyll, starch, raphides, alewrone 
grains, and crystalloids, now require description. 
CHLOROPHYLL AND CHLOROPHYLL GRANULES. a. Chlorophyll. 
This is the colouring material which gives to leaves their 
well-known green appearance. its chemical composition, owing 
to the great difficulty there is of obtaining it pure, is not posi- 
tively known ; but there seems much reason to believe that it is 
closely allied to wax. It is not soluble in water, but is readily 
so in alcohol, ether, or benzole. By soaking leaves in any of 
these substances a beautiful green solution is obtained when 
viewed by transmitted light, but which is red when observed 
by reflected light. If a weak alcoholic solution of chlorophyll 
is shaken up with an excess of benzole, the mixture separates 
into two distinct layers, the upper one of benzole which is 
coloured bright green, and the lower one of alcohol which is 
coloured bright yellow ; by which it would seem that chlorophyll 
is not a simple substance, but is a mixture made up of two or 
more colouring principles. Thus, according to Frémy, chloro- 
phyll is composed of two colouring principles—one blue, called 
phyllocyanin, and the other yellow, termed phyllozanthin ; while 
the more recent investigations of Michell, Stokes, Miller, 
Pringsheim, and others, render it probable that chlorophyll is 
even a more complex substance, as will be described hereafter 
when treating of the Physiology of Plants. 
In many fruits, such as the Cherry, Tomato, and common 
Arum, the chlorophyll of the pericarp becomes first changed to 
yellow and then red, as the fruit approaches maturity. In many 
plants, such as the brown Seaweeds, e.g. Fucus, the green chloro- 
phyll is obscured by an olive-green pigment, melanophyll ; or 
again in the red Seaweeds, such as Ceramium, by a red pigment, 
phycoerythrin. In these cases the pigments are more readily 
soluble in alcohol than the chlorophyll, so that by steeping 
portions of the plants for a short time in spirit, the colouring 
matters which veiled the chlorophyll are dissolved out, and the 
