ORGANS OF NT7TRITI0N. 



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•cells then elongate by their own inherent Fig. 222. 



vitality, by which the tissue constituting the 

 apex b is pushed onwards, and gradually 

 perishes, or is thrown off; the innermost 

 of these newly formed cells then remain 

 unaltered, while others immediately within 

 the point of the root continue to multiply 

 by division and grow in a similar manner 

 to the former, by which the layer of tissue 

 at the apex is again pushed forward and 

 perishes in like manner as before; then 

 new growth commences as in the former 

 instance, to be followed by similar changes. 

 Roots do not grow, therefore, throughout p^g_ 222. Young root of 

 their entire length like stems, but only a Maple magnified, a. 

 SI within their extremities, which are con- i^^lkuig phf/e^. ^b^TUe 

 tinually pushed forward and renewed. Thus original extremity, 

 the apex of the root is always clothed by a ^^ ^^^' 



layer of denser tissue than that which is within it. This layer 

 is termed by some botanists the pileorhiza. It forms a sort of 

 protecting shield to the young extremity of the root. The ex- 

 tremities of the root were formerly regarded as special organs, 

 and called spongioles or spongclets {fig. 223, sp), under the idea 

 that they absorbed fluid for the use of the plant, in the same 

 manner as a sponge sucks up water. But it will be seen from 

 the above description of the growth of roots that such structures 



(- 



V 



Fig. 223. 



Fig. 224. 



V 



i^fif. 223. Highly magnified vertical section of an Orchis root. sp. So- 

 called spongiole. c, c. Parenchymatous cells, fv. Wood-cells and vea- 

 selB. Fig. 224. Fibrils or root-hairs on the surface of a young root. 



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