CHLOROPHYLL GRANULES.—STARCH. 29 
presence of chlorophyll made manifest. Again, in some of the 
lower plants, such as Oscillatoria and Nostoc, there exists a blue 
pigment, phycocyan ; this may be obtained by soaking well- 
bruised specimens in cold water, to which it imparts a beautiful 
blue colour when viewed by transmitted light, and a beautiful 
red when seen by reflected light. 
b. Chlorophyll Granules.—It is not to be supposed that the 
chlorophyll exists indiscriminately in every part of the cell, for, 
on the contrary, it is confined to special portions of the proto- 
plasm which have been differentiated from the general mass. 
These portions of protoplasm are the so-called chlorophyll 
granules or chlorophyll grains, or, as they are also termed, 
chlorophyll bodies and chlorophyll corpuscles ; hence these struc- 
tures are granules of protoplasm coloured by chlorophyll. 
These granules appear as soft, doughy, more or less rounded 
masses, which are always enveloped by the surrounding proto- 
plasm and never lie loose in the cell cavity. Ifa plant is grown 
in the dark or etiolated, these granules remain pale coloured ; 
but if it is exposed to sunlight, they speedily become coloured 
green by chlorophyll (hence light is necessary, with rare ex- 
ceptions, for the formation of chlorophyll) ; and when so coloured 
they have the power of breaking up the carbon dioxide of the 
air or the water in which they are growing, and, returning the 
oxygen to the air, retain the carbon, which they are able to 
mix with the elements of water in such proportions as to build 
up a molecule of starch, C,H,,O., and some other carbo- 
hydrates. This process of building up starch and other carbo- 
hydrates out of the carbon dioxide of the air or water has been 
termed assimilation. (See ‘ Formation of Organic Compounds 
by Leaves,’ in the Physiology of Plants.) 
It has been said that chlorophyll is confined to the proto- 
plasm forming the chlorophyll granules; this is true in all the 
higher plants, but there are some plants amongst the lower 
orders in which the green-coloured portions form plates or 
spiral bands, as in Spirogyra ; or the whole protoplasm, with the 
exception of the ectoplasm, may be capable of being coloured, 
as in Gleocapsa and Oscillatoria. 
Srarcu.—There is no substance contained in the cells which 
has given rise to more discussion as to its origin and nature 
than starch. It is, with the exception of protoplasm, the most 
abundant and universally distributed of all the cell-contents, 
occurring as it does, more or less, in all parenchymatous cells 
(fig. 45) except those of the epidermis. In its fully developed 
state it is, however, most abundant in the matured structures 
of plants, as the pith of stems, and in seeds, roots, and other 
internal and subterranean organs which are removed from the 
influence of light. In these respects it presents a marked con- 
trast to chlorophyll, which, as we have seen, occurs only in 
young and vitally active structures placed near the surface of 
plants, and directly exposed to light. 
