CUPULIFERAE 379 



Kerner, loc. cit. ; Schulz, Ber. D. bot. Ges., Berlin, x, 1892; von Wettstein, Verb. 

 Zool.-Bot. Ges., Wien, xl, 1890, pp. 68-79.) — MacLeod says that the S catkins of 

 this species are larger than the 5, the latter possessing a more flexible axis than the 

 former. Schulz observed occasional hermaphrodite flowers, and von Wettstein found 

 entirely male and entirely female specimens. 



2572. B. pubescens Ehrh. (= B. alba L., according to the Index Kewensis). — 

 As the preceding species. 



2573. B. nana L. (Abromeit, ' Bot. Ergeb. von Drygalski's Gronlandsexped.,' 

 p. 77 ; Andersson u. Hesselman, 'Bidrag till Kanned. om Spetsbergens o. Beeren 

 Eil. Karlvaxtflora/ p. 667.) — Vanhoffen (cf. Abromeit, loc. cit.) describes the dwarf 

 birch as being among the less fragrant plants of Greenland. In Spitzbergen 

 (23. 7. '98) it was found growing, and bearing numerous S and 5 catkins, in a low 

 sheltered branch of Advent Bay Valley. A specimen collected by Bjorling (26. 7. '90) 

 possessed well-developed but seedless fruits (cf. Andersson and Hesselman, loc. cit.). 



807. Alnus L. 



Flowers anemophilous ; monoecious ; sometimes hermaphrodite. 



2574. A. glutinosa Medic. (Bail, Bot. Ztg., Leipzig, xxviii, 1870; Schulz, 

 Ber. D. bot. Ges., Beriin, x, 1892; Kerner, loc. cit.; Kirchner, ' Neue Beob.'; 

 MacLeod, op. cit., pp. 121-3.) — ^^'1 ^nd Schulz state that hermaphrodite flowers 

 are not rare in this species ; they are at least much more frequent than in Betula. 

 Kirchner describes the stocks as protandrous, the stigmas not maturing until the 

 $ flowers have withered. Kerner, however, says that they are protogynous, the 

 5 flowers maturing before the $. MacLeod states that the S and 5 catkins mature 

 simultaneously, and appear before the leaves. The 5 catkin possesses a long flexibl 

 axis, which can be set in motion by the wind ; this bears the flowers in groups of 

 three. The $ catkins are much smaller, the flowers being arranged in pairs. 

 Warnstorf describes the pollen-grains as pale yellow in colour, decahedral with blunt 

 angles, 31 /<, in diameter, smooth, with five germinating processes. 



2575. A. viridis DC. — Kerner states that the 5 flowers of this species mature 

 4-5 days earlier than the S ones on the same plant. 



cm. ORDER SALICINEAE RICH. 

 808. Salix L. 



Literature. — Sprengel, 'Entd. Geh.,' pp. 437-8; Herm. Miiller, 'Fertilisation,' 

 pp. 524-6; Kerner, 'Nat. Hist. PI.,' Eng. Ed. i, II, pp. 313-14; MacLeod, Bot. 

 Jaarb. Dodonaea, Ghent, vi, 1894, pp. 128-9; Knuth, ' Grundriss d. Bliitenbiol.' ; 

 Heinricher, Sitz.-Ber. Ak. Wiss., Wien, Ixxxvii, 1883. 



Flowers entomophilous ; dioecious ; with half-concealed nectar. The methanism 

 of willows is the simplest found among insect-pollinated forms. Although the flowers 

 are insignificant they are rendered conspicuous by being aggregated into catkins, 

 especially as these generally appear before the leaves unfold. Both the more con- 

 spicuous J flowers (which are therefore the first to be visited by insects), and the 5, 



