NUTRITION : WOLFFIA. 



315 



the base, and thus the plant continues to extend. The plant occurs in ponds 

 and ditches and is sometimes very common and abundant. It floats on the 

 surface of the water, ^^'hile the flattened part of the plant resembles a leaf 

 it is reallj' the stem, no leaves being present. This expanded green body is 

 usually termed a " frond. " A single rootlet grows out from the under side 

 and is destitute of root hairs. Absorption of nutriment therefore takes place 

 through this rootlet and 

 through the under side 

 of the "frond." 



595. Spirodela polyr- 

 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 



is very readily grown in aquaria. It reminds 

 one of a little insect as seen in fig. 413. There 

 are several rootlets on the under side of the 

 frond. Absorption of nutriment takes place 

 here in the same way as in lemna. 



596. Nutrition in wolffia. — Perhaps the most curious of these modified 

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



Fig. 413- 

 Spirodela polyrrhiza. 



Fig. 414- 

 Young frond of wolffia 

 growing out of older one. 



Fig. 415- 

 Young frond of wolffia 

 separating fro m older one . 



Fig. 416. 

 Another species o f 

 wolffia, the two fronds 

 still connected. 



flowering plants. Two species of this genus are shown in figs. 414-416. 

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



