SIMPLE ORGANS. 71 



see that the solid parts of vegetables are composed of a sub- 

 stance called by the common name of tissue. 



178. Tissue is divided into three kinds : cellular, woody y 

 and vascular. Cellular tissue is the fleshy part of fruits, 

 leaves, etc. It is composed of little cells, which adhere 

 together in very different degrees of closeness, sometimes 

 so loosely as to be easily separated from other parts, as in 

 very ripe fruits, the orange, for instance; and sometimes 

 cohering so firmly as to resist even the powers of an ordi- 

 nary magnifying-glass to demonstrate that it is not simple 

 membrane. 



179. Each cell is a little bag containing a liquid in the 

 early stage of its formation, but, changing with the growth 

 of the plant, it becomes firm, as in the wood of trees ; dry 

 and inelastic, as in the lamina of the leaf; hard, as in the 

 shell of nuts; sweet in the watermelon and sugar-cane, 

 acid in the lemon. Coloring matter is also deposited here, 

 and we have the Uue violet, the red rose, the golden sun- 

 flower, and the many-colored morning-glories. Here, too, 

 is deposited the material for the food of man, the amyla- 

 ceous material that makes the edible roots ; the substance 

 for bread, as found in corn, wheat, etc. ; the flour-like de- 

 posit in the leguminous tribes. 



180. If you cook an Irish potato over steam until it 

 bursts open, you will see a mealy mass, which under the 

 microscope comes out into regular bags or starch grains. 

 This is simply the cellular tissue distended to an unusual 

 size by the action of heat. 



181. In the quince and guava, little grains, hard like 

 seed, are found in the cellular tissue of the fruit. These 



178. This tissue is divided into how many kinds? Where is cellular tissue 

 found ? 



1 79. What is each cell ? How does it change with gi-owth ? What is deposited 

 here? Where is coloring matter deposited? Where food material ? 



180. What causes a cooked potato to appear mealy ? 



181. What are those hard particles found in the quince and guava ? What elsa 

 does sclerogen form ? 



