AQUATIC PLANTS OF SAN DIEGO.
Diisitm the wet Rpriog of 1884 I had an excellent op|>urtunJt)' to note the aquatic flora of this ^'icinity. Doubtless it seldom reaches such liisuriance : and in aome years, owing lo the scarcity of water, mauy of the plants cer- tainly make no appearance.
Surface-water reached an exceedingly low Atage in 1883 ; iind San Diego was supposed remarkably free from any water-plants, except the wide-spread Azolla, and a few other well- known apecies. However, the heavy rains of 1884. flooding the entire country, revealed a surprisingly large variety ; and that, too, where one would least expect it, — on the broad, usually dry and barren mesas.
The surface-geology of large portions of these mesas is characterized by innumerable hillocks, or email 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 de- pressions contain in stony places accumula- tions of cobblestones.
These innunierabte hollows naturally become miniature lagoons as soon as heavy rains com- mence ; and soon the leaves of Callitriche are floating u|K)n their surface, while the deeper portions of the little lakes are lined upon the bottom with large patches of Pilularia Ameri- cana. Tillaea angustifolia (Nutt.),and£latine; and along the borders are other minute plants which altogether form a tangled mat of minia- ture luxuriance, exceeding in comparison the vegetalioQ of the largest lakes. Some of the larger pools, longer covered with water, are filled along the e(.lges with junci, sedges and grasses, among which, at the bottom, Isoetes thrives as well as in the northern lakes.
Later in the season, Downingia pulchella and Pogogyne nudiuscula, with several less con- spicuous s.pecies, border the pools ; and still later a new golden Bloomeria, blue Brodiaeas. and other beautiful Liliaceae, arc found ; and these, in turn, give way to a few Compositae, preceding the next dry season.
This year another plant, Marsilia vestita, common to lagoons at high altitudes, and also Ammannia latifolia (L.) and Echinodius ros- tratus (Engelm.), grew abundantly in this vicinity, on the borders of a usuallj- dry flat. near the level of the sea. Other aquatics were found in great quantity throughout the country ; and nearly two dozen species of common water- plants, pre\-iouBly unknown to this section, were added to the local flora. C. R. Ohcittt.
��These is, we may remember, a p&siage in which Plato ioquirea what wuuld be the Ibougbis of a man who, having lived from jiiCancy under the roof of a cavern, where ihc light oatKide wai inferred ODly by its shadows, was brought (or Uie lirsl time into the full splendors of the sun. We may have enjojed the metaphor without thinking that it haa any physical appUcalinn to ourselves, who appear to have no roof over our heads, and to see the sun's face daily ; while the fact ia, that if we do not see that we have a roof over our heads in our atmonphere, and do not think of it as one, it is because it seem* so transparent nnd colorless.
Now. I wish to ask your atlentioii to-night to con- alderaLions In some degree novel, which appear to me to show that It is not transparent, as It appears, and that this teeming colortessneas is a sort of delusion of our senses, owing to which we have never in all our lives seen the true color of the sun, which is In reality blue rather than white, as it looks; so that tbla air all about and above us la acting like a colored !;1ass roof over our heads, or a sort of optical sieve, holding back the excess of blue in the original sunlight, and letting only the white sift down to lu. 1 will llrat ask you, then, to consider that this soem- ing colOrleasneBs of the air raay he a delusion of oar senses, due to habit, which has never given us any thing else to compare it with.
If that cave had been lit by sunsliine coining through a reddish glass In Its roof, would the pet^ petual dweller in it ever have had an idea but that the sun was red ? How is he lo know that the gloH Is > colored.' If he has never in his lite any thing to compare it with ? How can he liave any idea but that thi^ i-- the sum of all the sun's radiations (corre- Bponding toourideaof white orcolorless light)? Will not the habit of bis life confirm him In the idea that the sun Is rod ? and will be not think that there is no color In the gloM, so long as he cannot go outside to see ? Has this any suggestion for us, who have none of us ever been outside our crystal root lo see ? We must all acknowledge in the abstract, that habit is equally strong In us, whether we dwell in a cave or under the sky; that what we have thought from infancy will probably appear the sole possible expla- nation; and that, if we want to break Its chain, we should put ourselves, at least hi Imagination, under conditions where It uo longer binds ns.
The Cliallenger has dredged from the bottom of the ocean Bshes which live habitually at great depths, and whose enormous eyes tell of the correspondingly faint light which must have descended to them through the seemingly transparent water. It will not be so futile a speculation aa It may at first seem, to put ourselves la imagliintlon in the condition of creatures under the sea. and ask what the sun may appear to be to theip; (or, if the fish who had never
��by Prof. S .1'. I
��la of
��J
�� �
