938 



SCmNGE. 



LN. S. Vol. V. No. 129. 



sized in his paper on Alpine plants, and as 

 Lesage's work shows, great caution must 

 be exercised in discussing the morpho- 

 logical and physiological relations of species 

 which may grow in close proximity. Ger- 

 arclia maritima is * at home,' or tries to be, 

 on muddy saline banks, where it is usually 

 protected by the grassy vegetation around. 

 Though we call it a littoral plant, it is 

 modified differently from Cassia nictitans or 

 Yucca filamentosa, that may be its near neigh- 

 bors along sand bars. The mention of 

 Yucca can introduce us therefore to that 

 great assemblage that we now call desert or 

 xerophilous plants. 



At times met with in full view of the 

 ocean, they are most frequent and attain 

 their most varied development on desert or 

 volcanic areas. Let us linger for a little 

 over Yucca filamentosa. Along many miles 

 of the dry sandy ocean front of the Caro- 

 linas and Georgia it is a familiar plant. At 

 one season exposed to moist saline breezes, 

 at another to driving winds that hurl the 

 sharp sand particles against it, during a 

 large part of the year exposed to the full 

 glare of hot, sand-reflected sun rays, and 

 never enjoying a superabundance of mois- 

 ture, though its roots penetrate at least 

 five to six feet below the surface, it still sur- 

 vives and reproduces itself. But it is quite 

 different to the naked eye, and still more so 

 microscopically from the plant that we 

 grow in rich garden soil. Specimens from 

 the ocean beach have a dense, wiry aspect, 

 relatively short, broad, somewhat concave 

 leaves of a glaucous green hue and that 

 end in a hard mucro. Garden plants, on 

 the other hand, that have been cultivated 

 for many years and that may have been 

 themselves reproduced from garden seeds 

 or suckers, bear leaves that are long, nar- 

 row and soft leathery in texture, of a dark 

 green hue and with a soft mucro. Seed- 

 lings in the neighborhood of each type re- 

 produce their kind. 



No matter what the ancestral form may 

 have been or what its natural surroundings, 

 we must here admit acquired characters in 

 one of the types that are reproduced, and 

 our main concern again is to learn whether 

 such changes proceed in the life-time of an 

 individual or can gradually be acquired in 

 either direction by seed selection and prop- 

 agation. Such papers as those of Duchar- 

 tre*, Elliott, Hackel,J Lothelier,§ Sten- 

 strom,|| and notably that of Henslow,!! fur- 

 nish us with good evidence. For details 

 of Henslow's suggestive paper I would re- 

 fer you to the original, but Lothelier's 

 studies deserve comment. He varied his 

 experimental methods by making normal 

 air his xerophile environment, and saturated 

 air his new condition. 



He summarizes his results alike as to sun 

 and air exposure as follows: (a) stem and 

 leaf substance show a greater amount of in- 

 durated tissue in a xerophile state, a reduc- 

 tion of this in a moist atmosphere; (b) the 

 formation of leaf lobes, and, in such as pro- 

 duce them, of spines, is pronounced in a dry 

 atmosphere; (c) the epidermal cuticle is 

 increased, but the epidermal cells are re- 

 duced in size, the xylem is connected by a 

 continuous ligneous sheath, and the peri- 

 cycle is lignified in dry air, while in moist 

 air these features are feebly marked or ab- 

 sent. 



It is often stated, and in many cases 

 truly, that the battle in the vegetable world 

 is that of a plant against its neighbors, but 

 with xerophilous plants, that probably cover 

 one-sixth of the earth's surface, the struggle 

 is entirely one between the plant and its 

 physical or animal surroundings. Our na- 

 tive Opuntia has had its stem and branches 



* Bull. Soc. Bot. de France, 1885. 



t Trans. Bot. Soo. Edin., 1891. 



tVerband. d. K. K. zool. bot. Gesell. Wien, 1890. 



? Eev. Gen. de Botanique, Vol. 5, 1893. 



II Flora, 1895. 



II Jour. Linn. Soo. (Botany), Vol. 30, 1894. 



