326 



HOW CROPS GEOW. 



regular empty cells, the walls of which are, for the most 

 part, externally united and appear as one, a. At the points 

 indicated by b, cavities between the cells are seen, called 

 intercellular spaces. A slice across the potato-tuber, (see 

 fig. 52, p. 277,) has a similar appearance, except that the 



cells are filled with starch, 

 and it would be scarcely 

 possible to dissect them 

 apart ; but when a pota- 

 to is boiled, the starch- 

 grains swell, and the cells, 

 in consequence, separate 

 from each other, a practi- 

 cal result of which is to 

 make the potato mealy. 

 A thin slice of vegetable 

 ivory (the seed of PAy- 

 telephas macrocarpa), 

 under the microscope, dry or moistened with water, pre- 

 sents no trace of cell-structure, the cells being united as 

 one ; however, upon soaking in sulphuric acid, the mass 

 softens and swells, and the individual cells are at once 

 revealed, their surfaces separating in six-sided outlines. 



Form of CellSi — In the soft, succulent parts of plants, 

 the cells lie loosely together, often with considerable inter- 

 cellular spaces, and have mostly a rounded outline. In 

 denser tissues, the cells are crowded together in the least 

 possible space, and hence often appear six-sided when seen 

 in cross-section, or twelve-sided if viewed entire. A piece 

 of honey-comb is an excellent illustration of the appear- 

 ance of many forms of vegetable cell-tissue. 



The pulp of an orange is the most evident example of 

 cell-tissue. The individual cells of the ripe orange may 

 be easily separated from each other, as they are one-fourth 

 of an inch or more in length. Being mature and incapa- 

 ble of further growth, they possess neither protoplasm nor 



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