URTICACEAE 373 



Paul Mayer has examined numerous other species of Ficus and Sycomorus 

 (chiefly from herbarium specimens) and found Sycophaga and Blastophaga together 

 in some of them. 



792. Cannabis L. 



Flowers anemophilous ; dioecious. 



2554. C. sativa L. (Kerner, 'Nat. Hist. PI.,' Eng. Ed. 1, II, pp. 133, 143 ; 

 Heyer, ' Untersuchungen, &c.' ; Fisch, ' Zahlenverhaltnisse ' ; Warnstorf, Verh. hot. 

 Ver., Berlin, xxxviii, 1896.) — Heyer gives the ratio of male to female plants in this 

 species as 100 : 101-126, but Fisch says that it averages 100 : 154. Kerner states 

 that the anthers of male flowers do not dehisce until 4-5 days after the adjacent 

 female ones open ; the wind then shakes the pendulous anthers, and the pollen is 

 scattered ; this, however, can only be achieved gradually, the openings being extremely 

 narrow. Warnstorf describes a median streak on each side of each anther provided 

 with adhesive spherules before dehiscence. The pollen-grains are white in colour, 

 tuberculate, irregularly tetrahedral, 31-35 ft- in diameter. 



793. Humulus L. 



Flowers anemophilous ; dioecious. 



2555. H. Lupulus L. (MacLeod, Bot. Jaarb. Dodonaea, Ghent, vi, 1894, 

 PP- 374-6; Kerner, 'Nat. Hist. PI.,' Eng. Ed. i, II, pp. 133, 143.) — The stigmas of 

 the female flowers of this species are mature at least two days before the anthers 

 of adjacent male stocks dehisce, which they do in the same way as those of Cannabis. 

 Kerner and MacLeod compare the flower mechanism with that of Arrhenatherum 

 elatius and other grasses. Warnstorf (op. cit.) states that the anthers of the male 

 flowers are introrse, and beset externally in the middle line with yellow lupulin 

 granules. The pollen-grains are sulphur-yellow in colour, very irregular, smooth, 

 tetrahedral to polyhedral, about 25 /x in diameter. 



794. Moms L. 



2556. M. alba L. (Warnstorf, Schr. natw. Ver., Wernigerode, xi, 1896.) — 

 Warnstorf describes this species as anemophilous. The diclinous flowers mature 

 simultaneously. The greenish perianth leaves of the male spikes become reddish on 

 the outside when the pollen is mature. The mealy pollen-grains are white in colour, 

 very irregularly tetrahedral, about 20-5 /x in diameter. 



795. Broussonetia L'H^rit. 



2557. B. papyrifera Vent. (Kerner, 'Nat. Hist. PI.,' Eng. Ed. i, II, p. 137.) 

 — In this species the rather thick filaments lie in the bud Hke a bent watch-spring, 

 and suddenly straighten when the perianth expands, thus scattering the pollen into 

 the air. 



796, Ulmus L. 



Anemophilous protogynous flowers with persistent stigmas. Kerner says that 

 shortly before dehiscence of the anthers the filaments elongate to twice their original 



