140 The Great World's Farm 



ture of every portion of a plant from root to seed, and it 

 enters largely into the composition of the skeleton, or 

 frame-work, both of stems and leaves; for a plant's skele- 

 ton consists of fiber, identical in composition with the 

 fibers of the cotton and other plants used for weaving 

 purposes. 



Now both the skeleton and the flesh of a plant, every 

 part of it, indeed — roots, stems, leaves, flowers, fruit, 

 seed — consists either of a single cell, or of an assemblage 

 of cells, which may be compared with the cells of a honey- 

 comb, except that they vary extremely in size and shape. 



Some cells are so minute as to be altogether invisible 

 to the naked eye; as for instance, the spores of lichens 

 and fungi, the "germs" already mentioned, and certain 

 minute water-plants, each and all of which consist of a 

 single cell, filled, like the honey-cells, with more or less 

 fluid contents. 



But the cells in the flesh of a lemon are gigan:ic by 

 comparison, being half an inch long; the cells of fibers 

 are often much longer than this, and there are cells of all 

 sizes between these, the most usual size being from y^Vo 

 to -j^-Q of an inch across. Cells are of almost every pos- 

 sible shape, too — globular, square, six-sided, twelve-sided, 

 or quite irregular, with their outlines beautifully zigzagged 

 or waved. But whatever their shape and size, their 

 walls, thick or thin, are composed of the skeleton material 

 mentioned above, which is called after them "cellulose." 



This material, like cotton and other fibers, is composed 

 in great measure of carbon, and as all plants increase in 

 size by the multiplication of cells, it is evident that they 

 could not grow at all in air containing no carbon dioxide. 

 Neither can they grow if deprived of their leaves, for 



