66 



ELEMENTARY BOTANY. 



thickening has a reticulate or net like form (Fig. 99). In the 

 case of isolated cells, like pollen grains and spores, spines, 

 papillae, or ridges are occasionally developed. 



6. The important substance called leaf-green, or chlorophyll 

 (Gr. cMoros, green ; phyllon, leaf), is found in many cells of the 

 common plants. It is a green coloring matter which is solu- 

 ble in alcohol, ether, chloroform, etc. When it is removed by 

 these solvents a protoplasmic grain remains. Chlorophyll de- 

 velops in cells exposed to sunlight or electric light. Plants 

 with chlorophyll will gradually lose their color if placed in 

 the dark. The importance of this substance in plant nutri- 

 tion is evident from the fact that onlj' in cells containing 

 chlorophyll is mineral, or inorganic, matter changed — while 

 exposed to light — to organic, or vegetable material. Those 

 plants which are destitute of chlorophyll, for example the 

 Fungi and a few other plants, as Indian Pipe, Dodder, etc., 

 cannot live on mineral matter but must absorb their digested 

 food from living plants or decaying material. Such plants 

 can grow in the dark. 



Put in a vial of alcohol some bits of green leaves and in a day or two note 

 the solution of the chlorophyll. Cover up some green plants with soil or 

 put them in a dark room, or put a board over the grass, and after several 

 days note the bleaching, or disappearance of chlorophyll. Let potatoes 

 sprout in the cellar and the stems will remain white. 



7. Starch is formed in the chlorophyll-bearing cells. It is 

 always in the form of grains (Fig. 100). These are oval in 



the potato, elliptical in the bean, 

 elongated and very irregular in 

 Euphorbia splendens. They are 

 very small in corn, wheat, rice, etc. 

 The starch grains of the potato are 

 distinctly visible witli a good lens. 

 The average or commonest size, as 

 well as the shape, is constant in 

 each species of plant, but they vary 

 exceedingly in both these respects in different species. \\'Iien 



Fig. 100. 



