I2/I. West Americaji Scientist. 



These facts show that we have three distinctive elements in our 

 flora to be considered: that composed of species most hmited in 

 range, and therefore most characteristic; that which represents to 

 some extent the plants of the north and east; and third, the purely 

 aquatic element, which we would, naturally, expect to resemble 

 the last, but which more nearly approaches the first, at San Diego. 



During the wet spring of 1884, I had an excellent opportunity 

 to collect and note the aquatics of this vicinity. The preceding 

 year was unusually dry; few, if any, aquatic plants being able to 

 appear, from lack of their required element; and many of our wild 

 flowers were dwarfed or stunted or wholly discouraged from mak- 

 ing an appearance, or even an eflbrt to grow. 



No water plants had been reported from San Diego, except the 

 wide-spread Azolla Carolinianus — common to both Americas — 

 and a few other well-known species. 



But the heavy rains of the winter of 1883-4, especially during 

 the spring and late into the summer, flooded the entire country; 

 the rivers, usually 'bottom side up' filled their banks; every creek 

 overflowed; every depression or little hollow was changed into a 

 miniature lake or a wide-spreading lagoon* and springs of water 

 gushed forth in unheard of places. 



Especially on our mesas were to be found thousands of minia- 

 ture lagoons of large or small dimensions. The surface geology 

 of large portions of these mesas is characterized by innumerable 

 hillocks, or small, mound-like formations, rising from one to four 

 feet above the intervening depressions, and ranging from ten to 

 fifty feet in diameter. They are generally nearly circular, though 

 often irregular; and the depressions contain in stony places, ac- 

 cumulations of cobblestones. These innumerable hollows were 

 quickly filled by the persistent rains; soon the tiny leaves of Cal- 

 itriche marginata floated upon their surface, the long delicate 

 stems of the plant extending downward to the bottom, where they 

 were firmly anchored in the soil by a multitude of rootlets; the 

 deeper portions of the Httle lakes were carpeted on the bottom 

 with fields of the growing green of Pilularia Americana, a new 

 species of Isoetes, and other minute plants; while along the bord- 

 ers of the pools, large patches of Tillaea angustifolia and Elatine 

 sprung up and formed a tangled mat of luxuriant vegetation. 



Thus, the lakes were formed, their surface and bottoms grown 

 over with plants till the water was hid from vieW; and gradually 

 disappeared by evaporation, leaving only dense jungles on a 

 minute scale. The Callitriche and Elatine blossomed and bore 

 fruit; Pilularia and Isoetes ripened their spores, then 

 ' Withered away to let others succeed' 

 when another favorable season should chance to roll around in 

 future years. 



Some of the larger depressions, longer covered with water, were 

 filled along the edges withjunci, sedges and grasses, exceeding 



