SAXIFRAGEAE 



417 



narrowed near the mouth by stiff hairs projecting from the edge of the receptacle 

 and from the style, constituting a grating-like floor to the bell. The flowers are 

 also rendered more difficult of access to flies, and better adapted to bees by being 

 pendulous. The bells of R. nigrum are yet deeper, being almost spherical. They 

 too are pendulous, and are still better adapted to bees than those of the last species. 

 The flowers of R. sanguineum are tubular, though scarcely deeper than those of 

 R. nigrum (3 mm.). But owing to the erect position of the petals, the tube is 

 considerably prolonged (to more than 5 mm.). In spite of the tolerably erect 

 position of the flowers, they are usually visited only by bees. The last term of 

 the series is constituted by the flowers of R. aureum, which are in the form of 

 long tubes (10-n mm.). These are further prolonged some 3 mm. by the erect 

 petals, so that the nectar is only accessible to very long-tongued bees. Cross- 

 pollination by insects is secured by dioecism in the flowers of R. alpinum, but in 

 all the other species by the relative positions of stamens and stigmas, which are 

 successively touched by different sides of insect visitors. Since the hermaphrodite 

 species are homogamous, the possibility of automatic self-pollination is not excluded 

 in them. 



984. R. alpinum L. (Herm. Muller, 1 Fertilisation,' p. 249.) The flowers of 

 this species belong to class E. The greenish-yellow flowers are rendered con- 



FlG. 135. Ribes alpinum, L. (after Henri. Muller). (i) Female flower seen from above. (2) The 

 same in longitudinal section, seen from the side. (3) Do. of male flower, a, anthers; a', vestigial anthers; 

 n, nectary ; p, petal ; .?, sepal ; .?/, stigma ; si', vestigial stigma. 



spicuous by the sepals, under which the minute petals are almost completely hidden. 

 Hermann Muller describes the free upper part of the receptacle as forming a slightly 

 concave depression, in which nectar is secreted. The species is dioecious, the male 

 flowers being a little larger than the female ones, and of a yellowish-green colour. 

 They are therefore more conspicuous than the greener female flowers, and conse- 

 quently receive earlier visits. The female flowers possess vestigial stamens, and 

 the male ones a vestigial pistil. 



Visitors. Herm. Muller observed the following. 



A. Diptera. (a) Muscidae: i. Scatophaga merdaria /'. ; 2. S. stercoraria L. 

 {b) Syrphidae: 3. Syritta pipiens ., all three freq., skg. B. Hymenoptera. 

 Apidae: 4. Andrena albicans Mull. 5 and J, very freq., skg. and po-dvg. ; 5. A. 

 gwynana K. S, skg.; 6. A. parvula K. $, do.; 7. Halictus nitidus Schenck J, do.; 

 8. H. nitidiusculus K. 5, po-cltg. ; 9. Sphecodes gibbus Z. 5, skg. 



985. R. nigrum L. (Herm. Muller, 'Fertilisation,' p. 250; MacLeod, ' Nouv. 

 recherches sur la fertlsn. de quelques pi. phanerog.') The flowers of this species 

 belong to class C. They possess a characteristic odour, and Hermann Muller 



DAVIS. II Eg 



