206 THE PILLWORT. 



little more than one twelfth of an inch in diameter. 

 They are round and dark brown and contain four cells, 

 in each of which is a sorus bearing megasporangia and 

 microsporangia. From the shape of the sporocarps this 

 plant gets its name of " pillwort," while an allied species 

 is known abroad, by the name of " water-pepper," from 

 the same circumstance. 



Pilularia Americana has been found in a few localities 

 in California and Oregon, and is reported from Arkansas 

 also. It is quite likely that it grows in many other 

 places where its size and shape, so much like the imma- 

 ture rushes and sedges surrounding it, may aid it to go 

 undetected. This species has also been found in Chili. 

 An allied species is found throughout Europe. 



Mr. S. B. Parish, writing of the habitat of our species 

 in the Fern Bulletin, says : 



" In winters of abundant rainfall little pools form in the hollows of 

 the clay mesas about San Diego, and on the surface of these pools 

 and on their muddy margins these plants find a congenial home. 

 Often successive years pass with rainfall insufficient to maintain these 

 pools, and consequently without affording the pilularias an opportu- 

 nity for growth." 



The plants are thus apparently annuals, though all the 

 species of Marsiliaceae are regarded as perennials. 



