56 AQUATIC MICROSCOPY FOR BEGINNERS. 



mens in blossom. The flowers burst out of the mar- 

 gin of the frond, and consist of only those parts 

 needed to fertilize and to mature' the few small seeds. 

 The rootlets are valuable to the microscopist, as 

 they are favorite places for many just such creatures 

 that he most wants. The lower surface of the fronds, 

 especially of Lemna polyrrhiza, should be gently 

 scraped in a drop of water for certain Rotifers not 

 often found elsewhere. It is also much visited by 

 small worms, but not so frequently as the leaves of the 

 white water-lily. 



ANACHARIS CANADENSIS (Fig. 14.) 



This plant is readily recognized by the arrangement 

 of the leaves in circles, or whorls, of three each, two 

 of which are shown in Fig. 14. The stem is brittle, 

 and fragments .easily take root, so that the 

 plant spreads rapidly. Having been accidentally 

 introduced into England, it is said to 

 have grown so fast that it has choked 

 up some of the shallower streams and 

 to have become a nuisance. It is abun- 

 dant in this its native country, but it 

 never acts so badly here. The whole 

 plant is semitransparent, with leaves Ftg. 14.— An4- 

 about half an inch long springing directly f^"^^ '^^"^" 

 from the stem, and tapering to the point. 

 These leaves, under the microscope, exhibit a remark- 

 able phenomenon. 



All plants are formed of cells, or cavities of various 

 sizes and shapes, surrounded on all sides by a delicate, 

 membrane called the cell-wall. The cells are seldom 

 empty during life. Their contents are chiefly the 



