46 
MORPHOLOGY OF THE CELL. 
It is only in the Algae that the forms of the chlorophyll-bodies show much 
variety. In them it is frequently the case that the whole protoplasm-mass, with 
the exception of an outermost layer or a little more than this, either appears 
homogeneously green (as many swarm-cells, Palmellacese, gonidia of Lichens) ; or 
the chlorophyll- bodies assume stellate forms {e.g. Zygnema cruciatum. Fig. 43), 
or they form several lamellae with a stellate 
transverse section when the cell is cut across 
(as in Closterium, &c.), or straight or spiral 
bands {e.g. Spirogyra). But in most Algae, 
and in all Muscineae and Vascular plants, the 
chlorophyll-bodies are rounded or polygonal 
masses collected around a centre, and are 
termed Chlorophyll-granules. Generally a 
large number are contained in one cell ; some- 
times, however, only a few relatively large 
ones {e.g. Selaginelld), and in one of the Hepaticae of simplest structure {Anthoceros) 
only a single chlorophyll-granule exists in each cell, enclosing the nucleus; this 
therefore, when the cells divide, itself also divides in a corresponding manner. 
With extremely few exceptions Starch-grains arise in the homogeneous 
substance of the chlorophyll-bodies, and, where these have special forms, are 
distributed in definite places (see, e. g.^ Fig. 5, p. 10); they are produced, in larger 
or smaller numbers, in the interior of ordinary chlorophyll-granules. They are 
at first visible as points, gradually increase in size, and finally may so completely 
fill up the space of the chlorophyll-granule that its green substance is represented 
only by a fine coating on the mature starch-grain; even this disappears under 
certain circumstances (as in old yellow leaves of Pisum sativum or Nicotiana), and 
the starch-contents then lie in the cell, which now contains no protoplasm, in the 
place of the chlorophyll-granules. Sometimes drops of oil also form in the interior 
of the chlorophyll-body {e. g. in the bands of Spirogyra) ; and here and there 
granular contents of an unknown nature are observed. All these structures which 
arise in the chlorophyll-bodies are, however, not constant portions of them ; their 
appearance and disappearance depend entirely on light, temperature, and other 
circumstances; the appearance of the chlorophyll-bodies themselves is also bound 
up with these conditions of fife, to a description of which we shall recur in Book III, 
where it will be shown that chlorophyll is one of the most important elementary struc- 
tures, and that its contents are the products of its assimilation. The consideration 
of these and other purely physiological properties of chlorophyll must be deferred 
till then. Sooner or later, in the normal course of things, the chlorophyll-bodies 
are again absorbed ; this occurs in the most conspicuous manner at the time when 
the leaves of the higher plants are preparing for their fall; for instance, in the 
case of most of our native trees and shrubs, in the autumn. The whole proto- 
plasm-mass — and with it the chlorophyll-granules from the cells of the leaves about 
to fall — is then absorbed and transferred to the perennial persistent structures. 
The phenomena which accompany this process vary greatly ; but finally there 
remain in the cells filled with water and often with acicular crystals, a number 
of yellow glittering granules which bear no resemblance to chlorophyll ; if the falling 
Fig. 43. — A cell of Zyg7ie7na criiciatiini, with two 
stellate chlorophyll-bodies which are suspended in the 
interior of the cell ; they are united by a colourless bridge 
of protoplasm in which lies a nucleus ; the rays which form 
tlie union with the primordial utricle are nearly colourless 
in the middle. In each of the two chlorophyll-bodies 
lies a large starch-grain (X 550). 
