228 BOTANICAL GAZETTE. 



selves a good supply of carbon by keeping under all competitors by their close 

 ufts , e. g., Pkmtago major. 



III. Origin- of Types. — There are two ways, according to Herbert Spencer, 

 in which a stem may be developed from stalkless creeping fronds : first, by the 

 inrolling or folding of the fronds forming a tube with adnate edges and result- 

 ing in the endogenous stem and monocotyledonous embryo ; second, by the 

 thickening and hardening of a fixed series of midribs, resulting in an exogen- 

 ous stem and dicotyledonous embryo. Monocotyledonous leaves tend to show 

 little distinction between blade and petiole, to assume a lanceolate or linear 

 shape and parallel venation, because the fibrovascular bundles will tend to run 

 continuously over every part, since the leaves are mere prolongations of thestem- 

 forming portion, and because this venation is most convenient for long, narrow 

 leaves. Of dicotyledonous leaves the opposites are true. The central type of 

 leaf among monocotyls is long, narrow and rather fleshy ; among dicotyls, 

 simple, ovate and nearly ribless, or with faint digitate venation. Pinnate ve- 

 nation replaced palmate whenever circumstances caused leaves to lengthen 

 faster than they broadened, the main ribs then being given off, not from the 

 same point, but a little in front of one another. Pinnate ribs seem especially 

 adapted to forest trees, probably protecting them against storms. The shapes 

 of leaves thus depend upon two factors: first, the ancestrally inherited pecu- 

 liarities of type and venation ; second, the actual conditions to which the spe- 

 cies is habitually exposed. 



IV. Special Types. — Sessile leaves are particularly apt to be lanceolate. 

 Decurrent leaves show the traces of the primitive unity of stem and leaf. Rad- 

 ical leaves, with long foot stalks, will commonly be orbicular cordate and are 

 most frequently produced from perennials with richly-stored root-stocks. The 

 shapes of the leaves of climbers and trees have reference only to exposure to sun- 

 light. Unequal exposure causes them to become oblique, e. g., Begonia and 

 Tilia. Growth in dry soil and proximity to the sea, whether the plant grow in 

 sand or mud, both tend to produce succulence. C. R. B. 



EDITORIAL NOTES. 



The Report op the Botanical Section of the Acad. Nat. Sci., Philad., 

 for 1882, makes a good showing for the Herbarium, no less than .'5,346 species 

 having been added, one-third of which were new to the collection, and 100 of 

 the genera not before represented. This is the largest annual addition since the 

 organization of the Section, and is chiefly due to the zeal and liberality of 

 Messrs. Redfield, Cauby, Parker, Martindale, Meehan and others. Dr. Gray 

 supplied more than 1,000 species, and Prof. Sargent furnished choice herbarium 

 specimens of some of our rarer trees and shrubs. All this has thrown much 

 labor on the Conservator, Mr. John H. Redfield, who has been abjy assisted by 

 the Philadelphia botanists above mentioned. 



