xvi] EQUILIBRIUM AND ASSIMILATION 207 



of a slight and tentative circumnutation in the seedling roots 

 of several ordinary terrestrial plants. When the radicles of 

 PhaseoluSy Vicia and Quercus " were compelled to grow and 

 slide down highly inclined surfaces of smoked glass, they left 

 distinctly serpentine tracks." 



Hildebrand^ has described a differentiation between absorb- 

 ing and anchoring roots in the case oi Heteranthera zosteraefolia. 

 He states that from each leaf-base two roots arise, one of which 

 remains short and branches freely, while the other grows rapidly 

 in length and serves for anchorage. Plants cultivated in England 

 do not, however, so far as the present writer has been able to 

 observe, show this distinction ; it would be interesting to know 

 whether other botanists, who have seen this species growing 

 in Brazil, can confirm Hildebrand's description. In the case 

 of Phragmites communis'^^ there is a similar differentiation be- 

 tween long, thick, unbranched mud-roots, and thin water-roots, 

 branched to the third degree. 



The roots of free-floating plants obviously do not serve 

 for anchorage, but they seem sometimes to perform a corre- 

 sponding role in preserving equilibrium; this is particularly 

 obvious in the cases of Lemna and Stratiotes. Aquatic roots 

 often exercise another function, which is more remote from 

 those generally assumed in the case of terrestrial plants 

 namely, that of assimilation ; their colour is sometimes quite 

 conspicuously green. In the Water Chestnut, Trapa natans^^ 

 the later roots, developed adventitiously below the leaf-bases, 

 are free-floating and branched. These feathery structures have 

 been supposed by some authors to be of foliar nature; this is 

 erroneous, although physiologically they correspond to the 

 divided leaves oi Myriophyilum *. It is an indication of the extra- 

 ordinarily acute mind of Theophrastus, the Father of Botany 

 (born B.C. 370), that he avoided the morphological pitfall which 

 has been fatal to so many subsequent writers, for in describing 

 Trapa he says, "quite peculiar to this plant is the hair-like 



1 Hildebrand, F. (1885). 2 p^llis, M. (19 16). 



3 Barneoud, F. M. (1848). * Goebel, K. (1891-1893). 



