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 cruciaium. Fig. 43), 



or they form several lamellae with a stellate 

 transverse section when the cell is cut across 





W/AV^hd^_ 



(as in Closlerium, Sec), or straight or spiral 

 bands {e.g. Spirogyrd). But in most Algae, 

 and in all Muscineae and Vascular plants, the 

 chlorophyll-bodies are rounded or polygonal 



l-'u;. 43.— A cell of Zyjpiema crucicxtuni, with two * ^ i. j -^ 



stellate chiorophyii-botiies which are suspended in the masscs collcctcd arouud a ccutrc, and avc 



interior of the cell ; they are united by a colourless bridge 



of protoplasm in which lies a nucleus ; the rays which form tcrmcd ChJorophylls^ramcIes. Gcncrallv a 



the union with the primordial utricle are nearly colourless . . "* 



in the middle. In each of the two chlorophyll-bodies largC nUmbcr arC COntaincd iu OUC CCll ; some- 

 lies a large starch-grain (X 550). ^ r I'll 



times, however, only a few relatively large 

 ones {e.g. Selaginelia), 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 Nicoiiand), 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 (<?. g. in the bands of Spirog)>ra) ; 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 life, 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 



