HOW PLANTS OBTAIN WATER. 2J 



"frond." A single rootlet grows out from the under side and is destitute 



Fig. 37- 

 Fronds of the duckweed (Lemna trisculca). 



of root hairs. Absorption of water therefore takes place through this rootlet 

 and through the under 

 side of the "frond." 



52. Spirodela poly- 

 rhiza. This is a very 

 curious plant, closely re- 

 lated to the lemna and 

 sometimes placed in the 

 same genus. It occurs 



in similar situations, and pi g 3 g 



is very readily grown in Spirodela polyrhiza. 



aquaria. It reminds one of a little insect as 



seen in fig. 38. There are several rootlets on 



the under side of the frond. Absorption of 



water takes place here in the same way as in 



lemna. 



53. Absorption in wolffia. Perhaps the most curious of these modified 

 water plants is the little wolffia, which contains the smallest specimens of 

 the flowering plants. Two species of this genus are shown in figs. 39-41. 

 The plant body is reduced to nothing but a rounded or oval green body, 

 which represents the stem. No leaves or roots are present. The plants 

 multiply by " proliferation," the new fronds growing out from a depression 

 on the under side of one end. Absorption takes place through the surface 

 in contact with the water. 



54. Absorption by land plants. Water cultures. In connec- 

 tion with our inquiry as to how land plants obtain their water, it 



