AQUATIC PLANTS USEFUL TO THE MICROSCOPIST. 61 



roundings Rhizopods (Chapter IY.) and Infusoria (Chap- 

 ter "V.) are found in abundance. For the former it is 

 an unfailing source of supply. The water pressed out 

 of a little pinch of the moss will be sure to contain 

 many individuals and species. From a single small 

 bunch Dr. Leidy, when studying the Rhizopods, ob- 

 tained thirty-eight species and many individuals of those 

 animals, besides numerous active diatoms (Chapter III.) 

 and desmids (Chapter III.). 



The leaves make exquisite microscopic objects, on ac- 

 count of their curious and beautiful structure. Each 

 leaf is formed of two kinds 

 of cells, a and & (Fig. 15). 

 The large ones, a, will, 

 when magnified, immedi- 

 ately attract the attention. 

 They are hollow, and usu- 

 ally empty, and they have 

 a spiral thread running 

 around the walls. At cer- 

 tain stages of growth the 

 cell -wall also has one or 

 more small openings, c, 

 so that the water is able 

 to pass in and fill the cell. 

 This may explain why the Fig " 15 - p - tio of Leaf of sphagnum, 

 plant retains moisture for so long, and why it is so 

 easily wetted. 



The second kind of cells, 5, are found between the 



