LI. CASTANEACE^. 



I. BIECH SEEIES. 



It is not with the Chestnuts^ from which it received its 



name 



Betula pumila. 



more than a century since, that we shall commence the study of this 

 family, inasmuch as they represent a type with 

 inferior ovary and complicated by the presence 

 of an involucre quite peculiar, but with the 

 Birches^ (fig. 146-157), of which the gynse- 

 cium is superior and the flowers regular ape- 

 talous and monoecious. The males are often 

 tetramerous, and the calyx may then, as in 

 B, pumila'^ (fig. 146-150), be formed of four 

 sepals. They are rarely equal in that case ; 

 much more frequently the anterior is more 

 developed than the three others, which are 

 themselves unequal. These latter may even 

 disappear in great part or completely, as in 

 neighbouring species. The androecium is re- 

 presented by four elongate extrorse cells de- 

 hiscing by a longitudinal cleft.^ According to 

 certain authors, there are as many unilocular 

 anthers ; according to others (and this opinion 

 ought probably to be adopted) there are only 

 two anthers primarily superposed to two of 

 the sepals, the anterior and posterior, the 

 cells of which are quite separate, because 

 each of these cells is supported by one of 



Fig. 146. Foliaceous and 

 floriferous branch. 



1 Betula T, Inst. 588, t. 360.— L. Gen. n. 

 1070.— J. Gen. 409. — G^rtn. Fruct. ii. 54, t. 

 90, fig. 2.— Lamk. Bid. i. 452; Suppl. i. 

 686; III. t. 760.— TuRP. Bid. Sc. Nat. Atl. t. 

 301. — Spach, Revis. Betulac. Ann. Sc. Nat. ser. 2, 

 XV. 182 ; Suit, a Buffon, xi. 145. — Nees, Gen. 

 fasc. 4, t. 18.— Endl. Geu. n. 1840 ; Suppl. iv. 

 p. ii. 19. — Payer, Bull. Soc. Bot. de Fr. v. 151 ; 

 Fam. Nat. 161. — Kegel, Monogr. Betul. 9 ; BC. 



Biodr. xvi. sect. ii. 161. — H. Bn. Recherchet 

 Organogeniques sur les Amentacees {Compt. Rend. 

 Assoc. Franq. (1875), 756, t. 11, 12; Adam. xii. 



1). 



2 L. Mantiss. 124.— Reg. Prodr. 173. 



3 The pollen is flat, ellipsoid, somewhat tri- 

 angular, with three small pores and large halos. 

 (H. MoHL, Ann. Sc. Nat. ser. 2, iii. 312). 



