18 



PHYSIOLOGY OF NUTRITION. 



upper side of the thallus of a tissue rich in chlorophyll. Theii 

 comes a middle layer poor in chlorophyll, and on the ventral side 

 we find again two layers of cells richer in chlorophyll. 



If a leaf from a bud of Elodea canadensis is mounted on the 

 slide in a drop of water and examined microscopically, we shall 

 find after a short search cells which present the relations repre- 

 sented in Fig. 5, The parietal plasma, the nucleus-containing 

 mass of protoplasm, and the protoplasmic threads proceeding from 

 the latter, are easy to see. Frequently the protoplasm exhibits 



fairly active movements, and 

 in the plasma the chlorophyll 

 bodies stand out distinctly. 



If the outer layers of cells 

 are removed from the lower 

 side of an Echeveria leaf, 

 and we examine sections of 

 the loose tissue lying below, 

 we shall perceive in the un- 

 injured cells large chloro- 

 phyll grains, which are par- 

 ticularly interesting, inas- 

 much as, when examined 

 under fairly high magnifica- 

 tion, they exhibit compara- 

 tively well a foamy structure. 

 We may assume that all 

 chlorophyll grains possess 

 such a structure ; it is how- 

 ever by no means always easy 

 to make out. 



If Lupin seeds are germi- 

 nated in the light, the cotyle- 

 dons, appearing above ground, assume a green colour. Microscopic 

 investigation of a transverse section of a cotyledon at once reveals 

 the epidermis, the ground tissue, and the vascular bundles, and in 

 the cells of the ground tissue, especially in the peripheral ones, 

 are to be recognised many relatively large chlorophyll grains. 1 



It is of importance to emphasize here the fact that there are 

 many plant structures which do not appear chlorophyll-green, 

 but which still contain larger or small quantities of chlorophyll, 

 and are therefore capable of assimilatory activity. We prepare 



FIG. 5. Cells from the leaf of Elodea cana- 

 densis: a to e, cell-nucleus; /, protoplasmic 

 bands ; g, chlorophyll grains, some in a state 

 of division, and containing starch grains. 

 (After Kny.) 



