16 PHYSIOLOGY OF NUTRITION. 



5. The Chlorophyll Bodies. 



The chlorophyll bodies are to be regarded as organs of assimi- 

 lation. Their form is usually discoid ; in the cells of many 

 algae chlorophyll bodies of other forms occur. We take for 

 example a few threads of an alga which frequently occurs in stag- 

 nant waters, viz., a species of Zygnema, place them on the slide 

 in a drop of water, cover with a cover-glass, and examine under 

 a magnification of about 500 diameters. It is seen that each 

 filament is made up of a row of cells, and that in each cell 

 there are present two green, star-shaped structures, the chloro- 

 phyll bodies. We also see the cell-nucleus in the middle of 

 each cell. 



The various kinds of Spirogyra are algae which mostly occur 

 in stagnant waters, and consist of unbranched filaments of cells. 

 In each cell we perceive on microscopic examination green spiral 

 bands, varying in number in different kinds, which constitute 

 the chlorophyll bodies. The parietal plasma and the nucleus sus- 

 pended in the cell-sap by means of thin plasrnic threads are often 

 easy to observe. It may further be noted that at intervals in the 

 bands of Spirogyra are embedded spherical colourless structures, 

 the amylum bodies, which enclose a pyrenoid of angular contour 

 composed of proteid substances. The pyrenoids are surrounded 

 by numerous small starch grains. 



Once we have found good Spirogyra material, we should at- 

 tempt to cultivate it, since it is required for many physiological 

 experiments. It is best to proceed according to the method of 

 Strasburger. The algae are transferred to vessels, not too deep, 

 containing spring water. The walls of the vessels must either be 

 non- transparent, or rendered opaque by pasting black paper over 

 them. We expose the algae to bright diffuse daylight (not to 

 direct sunlight), and from time to time drop into the water small 

 fragments of peat which have been boiled and then soaked in the 

 ordinary food solution used in water culture experiments. 



Species of Cladophora, algae with branched filaments rough to 

 the touch, are frequently present both in standing and running 

 waters. The lateral branches spring from the upper end of the 

 cells. Fairly high magnification is employed for further investi- 

 gation, and it then appears that the green parietal layer of the 

 cells is composed of small polygonal structures which are sepa- 

 rated from one another by delicate colourless lines. The chloro- 



