SOME NOTES ON AZOLLA. 



BY DOUGLAS HOUGHTON CAMPBELL. 



One of the most interesting of the native Pteridophytes of Califor- 

 nia is the widely distributed Azolla Jiliculoides,occ2is\ona\\y called 

 " water-fern." This pretty little plant is common in many localities, 

 and when found at all, usually occurs in great numbers, and often 

 covers extensive stretches of quiet water with a dense purple-red 

 mantle so thick that the water is completely hidden. Sometimes, 

 however, a pond that is completely covered with the plant, may, after 

 a few months, show no trace of it beyond a few decaying fragments 

 that have sunk to the bottom, or are entangled among the Lemna 

 and other floating weeds on the surface. Whether this sudden dis- 

 appearance is due simply to the plant's having completed its natural 

 term of existence, or to some other cause, I am unable to say. A 

 pond near the La Honda road, some dozen miles back of Palo Alto, 

 was visited repeatedly between November 1891 and May 1892, and 

 at all times was covered with a luxuriant growth of Azolla. The same 

 pond visited in September, showed not a single living plant, although 

 ripe spores were found in the decaying masses of plants at the bot- 

 tom of the pond, and these germinated promptly when set free and 

 placed in clear water. The pond has not been visited since, so I 

 cannot say whether or not a new generation of plants has appeared. 



The genus Azolla is a small one, but widely distributed. Of the 

 four species usually recognized, tW' > are American, viz. : A. filicu- 

 loides and A. Caroliniana; A. nilotica is African, and A. pinnata is 

 Asiatic and Australasian. Both A. filiculoides and A. Caroliniana are 

 attributed to California, but all specimens yet seen by me have be- 

 longed to the former species, and as these included some from the 

 collection of the Academy of Sciences labeled A. Caroliniana., I have 

 some doubts about this species occurring here. This is the species 

 of the eastern part of the continent, where it is widely distributed 

 and reaches as far south as Brazil. A. filiculoides occurs in Chile 

 and Peru, and probably pretty much all along the Pacific Coast. 



As the life history of all the species was very imperfectly known, 

 an effort was made to clear up as far as possible the obscure points. 

 To this end observations were begun in November, i8gi, and con- 

 tinued, with more or less interruption, for a year. Only a few ol 

 the more important and general points brought out by these investi- 



