206 



ROOTS OF WATER PLANTS 



[CH. 



pression, " elles grimpent en bas." He adds that Potamogeton 

 densus (Fig. 137 G and //) shows the same peculiarity. A more 

 recent writer 1 has recorded that, when the turions of Pota- 

 mogeton obtusifolius germinate, they produce spirally coiled roots, 

 which apparently serve to anchor the plantlets in the mud. 



Twining roots are not confined to water plants; a case is 

 recorded by Darwin 2 , on the authority of Fritz Miiller, in 



FIG. 137. Twining roots of Zannichellia palustris, L. (AF) and of Potamogeton 

 densus, L. (G, H). [Hochreutiner, G (1896).] 



which the aerial roots of an epiphytic Philodendron in the forests 

 of S. Brazil, twined spirally downwards round the trunks of 

 gigantic trees. That root tendrils merely represent a further 

 development of the general tendency to nutation common to 

 stems and roots, is indicated by C. and F. Darwin's 3 record 



1 Graebner, P., in Kirchner, O. von, Loew, E., and Schroter, C. 

 (1908, etc.). 2 Darwin, C. (1891). 3 Darwin, C. and F. (1880). 



