PLANT-CELLS AND THEIR CONTENTS. 



2 93 



Fig. 6. Cross-Section of a Leaf, 

 showing the Cells containing 

 Chxorophyl. 



of the cells from the epidermis of the leaf no contents were apparent ; 

 in fact, the cells are tabular, very thin in proportion to their width, 

 and any contents they may possess are so nearly homogeneous as to 

 be transparent and invisible. But let us make a thin transverse sec- 

 tion of the same leaf. Here (Fig. 6) we find cells different in shape 

 from any we have yet seen, and evidently possessing different contents. 

 The cells from the inside of the leaf are here seen filled with tiny green 

 bodies, sometimes closely packed together, 

 sometimes scattered more sparsely. These 

 little green bodies are the chlorophyl-gr&n- 

 ules, affording to our vegetation all the 

 lovely tints which render charming a land- 

 scape in spring. Children of the light are 

 these little green grains, lovers and worship- 

 ers of the sun. At all events, they appear 

 by uncounted millions in the bright light of 

 the open sky, become fewer and fewer in 

 proportion as the light received by any 

 plant is diminished, and finally disappear 

 entirely when the plant is left in total darkness. Every one will recall 

 the appearance of potato-stalks where growth has started in some dark 

 corner of the cellar. Cells taken from such growth afford not a sign 

 of chlorophyl. Botanists tell us that the petals of flowers are only 

 altered leaves. In petal-cells, then, instead of chlorophyl-grains, we 

 find in some cases granules of yellow, sometimes of orange. Some- 

 times the cell contains no such granules, but rather some colored fluid, 

 red, blue, or purple, and then our flowers are tinted accordingly ; some- 

 times the cells of a petal contain air only, and then the flower is white. 

 But these tiny green grains in the leaf-cells do vastly more than 

 simply lend their color to the foliage ; they are readjusters and organ- 

 izers, and perform, in those diminutive laboratories we have been 

 calling cells, feats which the chemist strives in vain to rival. They 

 take possession of molecules of carbon dioxide and of water, compel 

 the binding chemical forces to relax their hold, combine again, to serve 

 the purposes of the plant, the atoms of carbon, of hydrogen, using 

 such part of the oxygen as may be necessary, and setting the remain- 

 der free in the open atmosphere all this in the sunlight. The chloro- 

 phyl bodies thus work while it is day, have charge of nearly all 

 the income of the plant, and provide in themselves for the temporary 

 storage, of its daily accumulations, mostly in the form of starch. When 

 the night comes, these same little factors give up at once their labors 

 and their stores, other cells of the plant begin to work, change and 

 transfer and change again, until all the wondrous series of vegetable 

 products with which we are familiar (the sugars, the oils, the alkaloids, 

 crystals of various forms and kinds) are formed and properly deposited. 

 We might go on now to examine cells containing many of these sub- 



