Traces of Unity in Plants. 2 1 



true root if it reach the ground ; and, to say the least, 

 the distinction between the aerial and terrestrial organ 

 can never be insisted upon. 



There are also certain passages in the life of a plant 

 which, taken in connection with the history of the tendril 

 and aerial root, may be appealed to as supplying evi- 

 dence to the same effect. 



Thus : many ordinary buds are developed as rootlets 

 if a branch be buried in the ground during the season of 

 growth. Thus : many points from which rootlets would 

 spring under ordinary circumstances are developed as 

 buds if a root be laid bare. Thus again : a branch, de- 

 nuded of its summer dress of leaves and flowers, may 

 be looked upon, at certain times, as an aerial root ; for, 

 as Biot pointed out first of all, the current of the sap 

 during frost sets, not from the spongioles to the branches, 

 but, in the contrary direction, from the branches to the 

 spongioles. 



The leaf-nature of the stem, moreover, is plainly 

 revealed in the Phyllocactus and in many other members 

 of the cactacean family. Here the stem is formed 

 from the quasi-leaves by a visible process of growth and 

 coalescence, and in a plant of ordinary dimensions may 

 be witnessed at one and the same time every gradation 

 between the green and flat and succulent leaf-like 

 organ, covered with rudimentary buds, and attached 

 only by a narrow neck to the parent-plant, and the brown 

 and woody and budless stem of which the constituent 

 elements or nodes have coalesced so perfectly as to 

 make it difficult to trace any longer the internodal lines. 

 In so far as concerns its shape, and the manner in which 

 the vessels are ranged upon its surface, the quasi-leaf of 

 the Phyllocactus must be regarded as a true leaf. It 

 differs from the ordinary leaf, no doubt, in bearing buds, 



