234 



NATURAL HISTORY OF PLANTS. 



number, are superposed to them. 



A liius eoi'difolia. 



Fig. 160. Trifloroua male 

 floriferous scale. 



]fig. 161. Male floriferous 

 scale, flowers removed. 



Earely the flower is 10-12- 

 merous and 10-12-androus.i 

 In the female catkin, ordi- 

 narily shorter, more rigid 

 than in the Birches, and 

 erect, there are only two 

 flowers in the axil of each 

 of the thick scales, the 

 middle one being abortive. 

 The gynsecium is similar 

 to that of the Birches, and 

 the fruit, 'dry and monospermous, is wingless or surrounded by a 

 membranoug wing. The axillant scales there become woody. The 



Alders are trees and shrubs of the 

 Ahius giutiiwsa. temperate and cold regions of both 



worlds in the northern hemisphere, 

 rare in South America and south- 

 ern Africa. Their organs of vege- 

 tation are analogous to those of the 

 Birches. The leaves are accom- 

 panied by lateral stipules. The 

 flowers are sometimes developed at 

 the same time as the leaves, but 

 more frequently earlier, and in this 

 case the females may, as in the 

 species constituting the genus 

 Ahaster,^ emerge from buds bearing one or more leaves. Often the 

 catkins are solitary, more rarely they are collected- in clusters. 

 About flfteen species of Alder are enumerated.* 



Fig. 165. Side view of 

 male floriferous scale. 



Fig. 166. Male flower. 



Fig. 167. Compound 

 fruit. 



' In A. nitida Endl. aud nepaknsis Don, 

 of which has heen made the genua Ckthi opsis 

 (Spach, Ann. Sc. Nat. ser. 2, xv. 183, 201). 



2 Spach, Ann. Sc. Nat. ser. 2, xv. 200 ; Suit. 

 a Buffon, xi. 244. 



3 Un these grounds Kegel divides the 

 genus into 4 sections: 1. Cletht-opsis (Ssi.cE.) . 

 Flowers developed at same time as leaves. 

 Male scalps uniflorous. Female flower 10-12- 

 merous. — 2. Alnaster (Endl.). Flowers pre- 

 cocious. Male catkins coming from 1-3-phyl- 

 lous buds. Scales 3-fiorous. Fruit with 

 membranous wing. — 3. PhyUothyrsiu (Spach). 

 Flowers developed at same time as leaves. 

 Scales 3-florous. Floral buds aphyllous. Fruit 



with membranous wing. — 4. Gymnothyrsus 

 (Spach). Flowers precocious. Scales 3-florou3. 

 Floral buds leafless. Fruit wingless or with 

 coriaceous wing. 



■• L. Spec. 1314 [BetuU). — G-A;RTsr. Fnict. ii. 

 64, t. 90 {Betula).—LiM-s.. Dict.i. 454 {Betula). 

 — Ait. Bort. Kew. iii. 139 (Betula). — Ehrh. 

 Beitr. 72 {Betula). — Mibb. Mem. Mus. xiv. 464, 

 t. 22.— W. Spec. iv. 334.— H. B. K. Nov. Gen. 

 et Spec. ii. 16.— DC. Fl. Franc, iii. 304.— 

 Don, Prodr. Fl. Nepal.', 68. — Bong. Mem. Pe- 

 ttrsh. ser 6, ii. 162. — Nctt. Syh. Atner. Suppl. 

 i. 34, t. 10.— Ten. Fl. Nap. Prodr. 64 ; Icm. ii. 

 340, t. 99.— Done. Ann. Sc. Nat. ser. 2, iv. 348. 

 — SiEB. et Zuco. Abh. Akad. Miinch. iv. Abth. 



