ON ROOTS. 27 



in water. In this state it is absorbed by the roots ; for 

 the root not only supports the plant by fixing it in the 

 soil, but affords a channel for the conveyance of nourish- 

 ment. If it does not fulfil this double office, it is not a 

 root, but a subterraneous branch. 



Caroline. But will not a branch, if placed under 

 ground, become a root, and absorb nourishment? I have 

 seen the gardener fasten down branches of laurel and 

 other shrubs, leaving only the extremity above ground ; 

 and these layers strike root, and become, in the course 

 of time, separate plants. 



Mrs. B. Striking root implies, that roots will (under 

 certain circumstances) grow from a branch, but the 

 branch itself cannot be converted into a root ; for at the 

 extremity of each fibre of a root, there is an expansion 

 of the cellular integument called a spongiole, from its re- 

 semblance to a small sponge, being full of pores, by 

 means of which the roots absorb the water from the 

 soil. Now, a branch, being destitute of this apparatus, 

 cannot supply the plant with nourishment. 



Caroline. True : It cannot feed without a mouth; but I 

 thought that there were pores in every part of a plant. 



Mrs. B. The pores in those parts of a plant above 

 ground are almost wholly for the purpose of exhalation. 

 The roots have no pores except in the spongioles at 

 their extremities, which, as I have observed, are for the 

 purpose of absorption. It would be very useless for 

 them to be furnished with evaporating pores, since they 

 are not exposed to the atmosphere, where alone evapor- 

 ation could take place. 



Emily. The tendrils of vines, then, and of other 

 climbing plants, which serve to fix them against a wall, 

 or the trunk of a tree, cannot be considered as roots ; 

 since, although they answer the purpose of sustaining 

 the plant, they are unable to supply it with nourishment. 



Mrs. B. Certainly, these plants are furnished with 

 roots which pump up nourishment from the soil ; .but there 



88. How does a subterraneous branch differ from a root 1 ? 89. 

 What does Caroline say she has seen the gardener do! 90. What is 

 to be understood by striking root, in botany! 91. What is a spon- 

 giole, and from what does it derive its name! 92. For what purpose 

 are those pores in plants above ground! 93. What are those parts 

 of climbing plants called, which fix them against a wall! 



