CUCURBITACEAE 



455 



as pollinators ; in the case of Benincasa cerifera, a humble-bee was also observed. 

 Lagenaria appears to be visited by crepuscular insects (presumably hawk-moths). 



The nectaries consist of a layer of secretory tissue about i mm. thick, and 

 are provided with water-stomata. The nectar results from the conversion of starch 

 into sugar (glucose) by means of the protoplasm or a special ferment (Solla, Justs 

 bot. Jahresber., Leipzig, xxi (1893), 1896, p. 335). 



312. Bryonia L. 



Flowers monoecious or dioecious, greenish-yellow in colour; with concealed 

 nectar, secreted as above described. Two pairs of filaments are fused, the fifth 

 is free. 



1079. B. dioica Jacq. (Herm. Miiller, 'Fertilisation,' pp. 268-70, ' Weit. 

 Beob.,' II, p. 210; Ludwig, Verh. bot. Ver., Berlin, xxvi, 1885, p. 21; Schmiede- 

 knecht, ' Apidae europ.,' I, p. 665 ; Knuth, ' Bloemenbiol. Bijdragen.') The female 

 flowers of this species are only 

 half as large as the male ones. 

 In the latter, according to Hermann 

 Miiller, the filaments spring from 

 the edge of the cup formed by 

 the fusion of the bases of calyx 

 and corolla, and they incline 

 together so as completely to 

 cover the cup. Three narrow 

 lateral passages covered by long 

 hairs lead between the filaments 

 to this nectary, and there is a 

 fourth access from above, running 

 down between the upper ends of 

 the filaments. The anthers dehisce 

 by long narrow clefts, curved in 

 such a way that for most of their 



length they are turned towards the lateral passages, while their uppermost parts face 

 directly upwards. An insect probing for nectar will therefore be dusted with pollen 

 either on the lower side of its body, or on both sides of its head, and in subsequent 

 visits to female flowers will effect pollination. The female flowers are only half 

 the size of the male ones, and are therefore usually visited later. The style projects 

 from the middle of the nectar-cup, and divides into three diverging branches. The 

 ends of these are very broad, lobed, and set with projecting points, so that an 

 alighting insect is obliged to touch them. Pollen is carried by visitors to a con- 

 siderable distance. F. Ludwig, for example, observed the crossing of a female 

 plant by pollen from a male plant 40 m. away. 



Visitors. The chief one is the bee Andrena florea F. 5 and S, which visits 

 the flowers of this species almost exclusively (Herm. Miiller, Schmiedeknecht). 

 A It is by far the commonest visitor, and appears to obtain all it requires in 

 the way of flower food from this plant alone' (Herm. Miiller). Schletterer 



Fig. 154. Bryonia dioica, L. (after Herm. Miiller). (i) and 

 (2) Anthers of male flowers. (3) A male flower in longitudinal 

 section ; enlarged. (4) The same, seen from above ; further 

 enlarged, a, filament; k, colourless spherules; , nectary; 

 /, pollen. The lateral nectar-passages are indicated by arrows. 



