ELEMENTS OF ORGANIZED STRUCTURE. 



247 



across a young cabbage-stalk. It exhibits the outline of 

 the irregular empty cells, the walls of which are, for the 

 most part, externally united and appear as one, a. At 

 the points indicated by #, air-filled cavities between the 

 cells are seen, called intercellular spaces. A slice across 

 the potato-tuber (see Fig, 52, p. 300) has a similar ap- 

 pearance, except that the cells are filled with starch, and 



it would be scarcely pos- 

 sible to dissect them apart; 

 but when a potato is boiled 

 the starch - grains swell, 

 and the cells, in conse- 

 ence, separate from each 

 // other, a practical result of 

 i(^ which is to make the po- 

 tato mealy. A thin slice 

 of vegetable ivory (the seed 

 of P h y t e I e p li a s macro- 

 carpa) under the micro- 

 scope, dry or moistened with water, presents no evident 

 trace of cell-structure ; however, upon soaking in sul- 

 phuric acid, the mass softens and swells, and the indi- 

 vidual cells are revealed, their surfaces separating in 

 six-sided outlines. 



Form of Cells. In the soft, succulent parts of 

 plants, the cells lie loosely together, often with consider- 

 able intercellular spaces, and have mostly a rounded out- 

 line. In denser tissues, the cells are crowded together 

 in the least possible space, and hence often appear six- 

 sided when seen in cross-sec tkm, or twelve-sided if viewed 

 entire. A piece of honey comb is an excellent illustra- 

 tion of the appearance 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. Being mature and 



Fig. 30. 



