SALICINEAE 389 



are abundantly visited and pollinated by these insects. Lundstrom (' Krit. Bemerk. 

 ii. d. Weiden Nowaja-Semljas ') asserts that the pollen of northern species of Salix is 

 not so sticky as that of others — owing to the possession of fewer droplets of oil — and 

 is therefore easily dispersed by wind. But the presence of nectaries, even in northern 

 species, is against exclusive anemophily. 



Visitors. — Herm. MUller observed a solitary butterfly. 



2592. S. retusa L. (Herm. Miiller, loc. cit. ; Kerner, loc. cit.) — In this species 

 also, according to Kerner, the female flowers mature some days before the male ones. 



Visitors. — Herm. Miiller observed a single wasp. 



MacLeod (Flanders) observed, in willows in which the flowers appear be/ore the 

 foliage-leaves, the honey-bee, 3 humble-bees, 18 short-tongued Hymenoptera, 

 4 hover-flies, 14 other flies, 2 beetles, and a moth (Bot. Jaarb. Dodonaea, Ghent, 

 vi, 1894, pp. 131-3); also, on species in which the flowers and foliage leaves appear 

 simultaneously, the honey-bee, 3 short-tongued bees, 6 hover-flies, and 3 other 

 Diptera (op. cit., p. 133). 



Schneider (Arctic Norway) observed the following 9 humble-bees on S. nigricans 

 Sm., S. glauca Z., S. Lapponum L., and S. phylicifolia L. — 



1. Bombus agrorum F., var. dLVCdcMS Acerbi ; 2. B. alpinus L.; 3. B. hypnorum 

 L.; 4. B. lapponicus F.; 5. B. nivalis Dalhb.; 6. B. pratorum Z. ; 7. B. scrim- 

 shiranus K. ; 8. Psithyrus quadricolor Lep. ; 9. P. vestalis Fourcr. 



809. Populus L. 



Flowers anemophilous ; dioecious. Pollen scattered, according to Kerner, as 

 in Juglans. 



2593. P. nigra L. (Warnstorf, Schr. natw. Ver., Wernigerode, xi, 1896.) — 

 In this species the yellowish bracts of the male spikes are glabrous at the margin, 

 slightly hollowed at the back, and provided with a low swelling round the edge, 

 which makes it difiicult for the pollen to slip down. The pollen-grains are pale- 

 yellow in colour, irregularly polyhedral, tuberculate, 30-40 ft. in diameter. 



Visitors. — Burkill (Yorkshire coast) observed the Muscid Onesia cognata Mg., 

 searching for nectar on S flowers (' Fertlsn. of Spring Fls.'). 



2594. P. tremula L. (Sprengel, ' Entd. Geh.,' p. 439.) — 



Visitors. — Sprengel saw the male flowers of this species visited on the 15th ot 

 March, 1790, at Potsdam by numerous pollen-collecting honey-bees; 'The male 

 trees could be recognized and distinguished from the female ones at some distance 

 by the loud buzzing of these insects.' 



2595. P. pyramidalis Salisb. (Herm. Miiller, ' Weit. Beob.,' II, p. 211.) — 

 Visitors. — Herm. MuUer (Thuringia) observed thousands of po-cltg. honey-bees. 



CIV. ORDER EMPETRACEAE NUTT. 

 810. Empetnim L. 



Dioecious, sometimes with protandrous hermaphrodite flowers. Warming 

 describes them as anemophilous, but Lindman as entomophilous. The latter 



