468 WILSON EXPEDITION TO CHINA 



The Himalayan and Yunnan forms are very much alike, and this species seems 

 to differ from B. cylindrostachya Spach in its more glossy and more or wholly 

 glabrous, longer and narrower leaves which are more distinctly acuminate and 

 also differ somewhat in the character of their serration. It may be possible to dis- 

 tinguish several forms, as Regel did, but I should like to see much more material 

 from India before making such an attempt. The fruiting catldns seem to be always 

 more slender than those of B. cylindrostachya Spach. 



4. Betula luminifera Winkler. See p. 455. 



5. Betula Baeumkeri Winkler in Engler, Pflanzenr. IV.-61, 91, fig. 22 D-F 

 (1901). — Schneider, III. Handb. Laubholzk. 11. 882, fig. 552 c, 553 i-k (1912). 



CHINA. Yunnan : without locality, J. Dclavay (type ex Winkler). 



Having seen so many specimens of B. luminifera Winkler, showing the varia- 

 bility of this species, 1 suspect that B. Baeumkeri, of which I have been unable to 

 see any material, may prove to be only a form of that species. 



Sect. 2. COSTATAE Regel in Bull. Soc. Nat. Mosc. XXXVIII. pt. 2, 412 

 (1865). — Prantl in Engler & Prantl, Nat. Pflanzcnfam. III. abt. 1, 45 (1887). — 

 Koehne, Deutsche Dendr. 107 (1893). — Schneider, III. Handb. Laubholzk. I. 98 

 (1904). 



Betula, sect. Euhetula Regel, subsect. Costatae Regel in De Candolle, Prodr. 

 XVI. pt. 2, 175 (1868). — Dippel, Handb. Laubholzk. II. 183 (1892).— 

 Winkler in Engler, Pflanzenr. IV .-61, 57 (1904). 



This section is rather an artificial one. It includes very different forms like B. 

 Schmidtii Regel and B. corylifolia Regel & Maximowicz, which may represent dis- 

 tinct groups. The latter species and B. grossa Siebold & Zuccarini (probably also 

 B. insignis Franchet and B. costata Trautvetter) are characterized in a living state 

 by the same peculiar odor of the inner bark of young branchlets found in that of 

 the American B. lenta Linnaeus and B. lutea Michaux, but it seems to me an un- 

 natural classification to bring together these species in one group on account of 

 this peculiarity which unfortunately cannot be detected in dried specimens with 

 certainty. I distinguish the following subsections to which we have to add sub- 

 sect. NiGRAE, nov. subsect. (including only the American B. nigra Linnaeus) and 

 subsect. Lentae, nov. subsect. (Sect. Lentae Regel in Bull. Soc. Mosc. XXXVIII. 

 pt. 2, 417 [1865]. — Sect. Euhetula, subsect. Lentae Regel, in De Candolle, Prodr. 

 XVI. 2, 179 [1868]), including only American species. I cannot accept the different 

 subgenera proposed by Nakai (in Tokyo Bot. Mag. XXIX. 40 [1915]). 



Subsect. a. Ermanianae Schneider, n. subsect. 



Betula, subg. Ermani Nakai in Tokyo Bot. Mag. XXIX. 41 (pro parte) (1915). 



The species united in this group seem to be closely related. They have a smooth 

 whitish or reddish or creamy bark peeling off in transverse flakes or strips. The 

 following species are well separated geograpliically, but it is not always easy to 

 distinguish them without sufficient judiciously collected material. What is needed 

 to estabUsh a good classification of a difficult genus Hke Betula are observations 

 of living plants in the field. 



5. Betula Ermanii Chamisso in Linnaea, VI. 537, t. 6, fig. D, a-e (1831). — 

 Erman, Reise um die Erde, Naturh. Atlas, 56, t. 17, fig. 2 (1835). — Spach in Ann. 

 Sci. Nat. ser. 2, XV. 190 (1841). — Ledebour, Fl. Ross. III. pt. 2, 653 (1850). — 

 Trautvetter in Mem. Sav. Etr. Acad. St. Petcrsbourg, IX. (Maxim.owicz, Prim. 

 Fl. Amur.) 252 (1859). — Regel m Nouv. Mem. Soc. Nat. Mosc. XIII. pt. 2, 120 

 {Monog. Betulac. 62), t. 6, fig. 35, 37, 38, t. 12, fig. 13-28 (excl. var. y) (1861); 



