30 



up to 35 cm. long and 8 mm. thick. At the nodes the runners 

 send out roots, usually in two lateral groups, also leaves, and 



* 



vertical stems bearing leaves and flowers, besides, branches that 

 develop into runners, forming frequently an extensively ramified 

 system. 



The secondary roots, arising at the nodes, are slender and 

 long, often reaching 30 cm. The older branch into numerous, 

 finally very thin rootlets provided with root hairs. At the tip of 

 every rootlet there is a sheath or case which looks exactly like 

 the finger of a glove. (Fig. i.) When placed in glycerin the 

 cells of the root contract somewhat, and the sheath becomes 

 more plainly visible. It consists of a single layer of elongated, 

 oblong cells, forming a distinct, firm membrane with an unbroken, 

 smooth rim, and extends on the main roots for a distance of over 

 2 mm. above their growing ends. The sheath is fully developed 

 at the tip of the forming rootlet, before it breaks through the 

 epidermal layer, which is raised, then bursts, and persists at the 

 base of the root, similar to the coleorrhiza of grass-seedlings. 



Although there can be no doubt that this sheath has to per- 

 form the same office as an ordinary root-cap, viz., to protect the 

 tender meristematic tissues of the root-end, its peculiar structure 

 tempts me to ascribe to it an additional function. The upward 

 strain exerted upon the stems and the entire root-system of our 

 plant by the agitated surface of the water and the buoyancy of 

 the plant itself with its floating leaves must be very great Indeed. 

 It seems to me that the innumerable sheaths at the ends of the 

 roots and their branches must assist the plant a great deal in re- 

 sisting that upward pull by acting somewhat like anchors. They 

 are easily pushed forward and downward into the loose muddy 

 soil along with the growing root-ends, but when pulled upward 

 they will evidently resist the strain in a most effective manner. 

 The fact that other aquatic plants have very similar root-caps 

 seems to corroborate this view. 



Otherwise the roots present no peculiarities. There is a cen- 

 tral, very thin plerom surrounded by thin-walled endodermls 

 cells; the other root-tissues are very loose, with large intercellu- 

 lar canals, and a thin epidermis. 



What is most remarkable in the strncture of the fnllv devel- 



