CHLOROPHYLL -GRANULES AND THE SUN'S RAYS. 373 



Chlorophyll-gi'anules appear to be imbedded in protoplasm from their origin 

 until their disaj^pearance. When the protoplasm is situated round the wall — or, in 

 other words, when the central cavity of the protoplasm is large and filled with 

 watery cell-sap, and the plasma which surrounds the sap-cavity is sac-like and only 

 forms a thin covering to the cell chamber, then the chlorophyll-granules are usually 

 imbedded in the middle layer of the parietal plasma, so that they are separated 

 from the sap-filled central cavity, as also from the cell-wall, by a layer of colour- 

 less protoplasm. The same thing occurs when the chlorophyll-granules are 

 imbedded in the plasma strands which are stretched across the cell -cavity (see 

 figs. 5^ and 5^). Frequently the chlorophyll-granules project like warts, and thus 

 give a knotty appearance to the protoplasmic strands; but even then they are 

 always covered by a thin colourless layer of pi'otoplasm. 



In spite of this close connection, chlorophyll-granules always appear to be 

 sharply defined, and exhibit in their entire development a certain separateness from 

 the protoplasm in which they may reasonably be supposed to take their origin. 

 They enlarge, divide, and multiply, and occasionally in the course of their life alter 

 their form. With respect to their shape there is little variety in the green tissue 

 of the stem and leaves of higher plants. The chlorophyll-granules almost always 

 appear there as rounded or occasionally angular, sometimes even as lenticular or 

 many-sided grains. A much greater diversity is observed in those simple green 

 plants which live in water, and have been classed together under the name of 

 Algag. In the cells of the green filaments of Zygnema, which are represented in 

 fig. m of Plate I., the chlorophyll bodies are stellate, and are so arranged in 

 each cell that there are usually two stars side by side. In species of the genus 

 Spirogyra (Plate I., fig. I) they form spirally wound, usually knotty, bands, and in 

 most species of the genus only one band in each cell; but in some species there are 

 two bands, whose spirals cross one another, whereby very ornamental structures 

 come into view mider the microscope. In species of the unicellular Penium 

 (Plate I., fig. k), the chlorophyll bodies form plates or bands parallel to the long 

 axis of the cell, projecting against the cell-wall in all directions. In Mesocarpus a 

 single green plate is observable, which divides the cavity of the cell into two almo.st 

 similar halves; (Edogoniwrn exhibits a latticed plate; species of the genus Ulva 

 have plate-shaped chlorophyll bodies which lie close to the wall; in the cells of 

 Podosira are seen disc-shaped chlorophyll bodies which jut out in all directions; 

 and in the liverwort Anthoceros the chlorophyll bodies are in the form of hollow 

 spheres surrounding the centres of the cells. 



The number of chlorophyll-granules in the protoplasm of the cell varies from 

 one to several himdreds. In the cells of selaginellas there are usually 2-4; in 

 those of the luminous moss, Schistostega osmundacea, to be described later more in 

 detail, 4-12 (Plate I., fig. p). The green cells of most leafy flowering plants contain 

 20-100, many even 200. In the cells of Vaiuiheria (Plate I., fig. a-d), the proto- 

 plasm is so crowded with tliickly-pressed small green granules as to make one 

 think that the whole cell-body contained but a single chlorophyll mass. Foliage- 



