[321] SCIENTIFIC MANUAL. 35 



The commonly accepted theory of spongeoles at the 

 extremities of growing roots, through which nourishment is 

 absorbed, is rejected by the best modern authorities on 

 vegetable physiology, after careful microscopic investiga- 

 tion. 



Prof. Gray says: "The root, however, does not grow 

 from its very apex, as is corcmionly stated ; but the new 

 formation (by continued multiplication of ceils) takes place 

 just behind the apex, which consists of an obtusely conical 

 mass of older cells. As these Wear away, or perish, they 

 are replaced by the layer beneath ; and so the advancing 

 point of the root consists, as inspection plainly shows, of 

 older and denser tissue than the portion just behind it. 



" The point of every branch of the root is capped in the 

 same way. It follows, that the so-called spongeoles or, 

 spongelets, of the roots, or enlarged tips of delicate forming 

 tissue, have no existence. 



" Not only are there no special organs of this sort, but 

 absorption evidently does not take place, to any considera- 

 ble extent, through the rather firm tissues ot the very point 

 itself." 



This "root-cap," the cells 'of which are filled with air, 

 instead of sap, protects the tender formative tissue, and 

 facilitates the extension of the root in the soil. 



Besides the forming tissue, near the extremities of the 

 proper roots, there are numerous " root-hairs " on the new 

 parts of the roots. These are the active agents in the 

 absorption of food from the soil. 



Roots do not increase in size so rapidly as stems, nor are 

 they so regular in their formation. They differ, also, from 

 stems in increasing in length only at their extremities, 

 while stems grow both by accretion at the end by the 

 formation of new buds, and by elongation of the tender 

 parts. 



The extreme attenuation of the advancing root greatly 

 facilitates its insinuation into the soil, while it enables it to 



