RHAMNEAE 



247 



Visitors. — At Kiel I only saw a hover-fly (Eristalis nemorum Z.), skg. Hoffer 

 observed Bombus hypnorum L. 5 in Steiermark. 



617. R. pumila L. (Herm. Muller, ' Alpenblumen,' pp. 169-71.)— The small 

 flowers of this species — which Kerner describes as possessing an odour of honey — 

 are said by Muller to be usually hermaphrodite, while Koch (' Synopsis ') describes 

 them as dioecious-polygamous. Cross-pollination is favoured in the hermaphrodite 

 flowers owing to the fact that the stamens and stigmas are on opposite sides of 

 the nectar. 



Visitors. — Herm. Muller observed Hymenoptera (Chrysididae, Formicidae), 

 beetles, and Diptera (Muscidae, Empidae, Syrphidae), in the Alps. 



6x8. R. saxatilis L. — Kerner describes this species as dioecious, with pseudo- 

 hermaphrodite pollen-flowers and fruiting-flowers. 



619. R. Frangula L. (=Frangula Alnus Mill). (Herm. Muller, ' Fertilisation,' 

 pp. 163-4, 'Weit. Beob./ II, p. 212; 

 Kirchner, 'Flora v. Stuttgart,' pp. 

 363-4; Warnstorf, Verb. bot. Ver., 

 Berlin, xxxviii, 1896; Schuiz, 'Bei- 

 trage,' I, p. 31, II, p. 61 ; Knuth, 

 ' Bloemenbiol. Bijdragen.') — The in- 

 conspicuous greenish-white herma- 

 phrodite flowers of this species, 

 according to the investigations of 

 Hermann Muller and A. Schultz, are 

 protandrous to a less (Thuringia) or 

 greater (Westphalia, South Tyrol) 

 degree. The cup-shaped calyx is 

 also a hemispherical nectary. Between 

 the five triangular whitish tips of the 

 sepals, are five small white bifid petals, 

 which almost cover the five inwardly 

 curved introrse stamens. In the base 

 of the calyx lies the short-styled pistil, 

 the bilobed stigma of which is at 

 a lower level than the anthers. At 

 the time when the latter are ripe the 

 stigma is still ill-developed. Insect 

 visitors usually effect cross-pollination while sucking nectar, since they touch 

 the anthers with one side of their body and the stigma with the other. As the 

 flowers, however, are rather inconspicuous, the number of visitors is small, and 

 automatic self-pollination is often effected as a last resort, the withering stamens 

 dropping pollen on the mature stigmas. 



The account given by A. Schuiz differs from that of Muller in some points. 

 He found that in plants growing at Halle and in North Thuringia, the petals are 

 never so deeply cleft as represented by Muller (see Fig. 76). He describes the 

 anthers as being enveloped for a considerable time by the white longitudinally 



Fig. 76. Rhamnus Frangula^ L. (After Herm. 

 Mailer.) I. Young flower seen from above. 2. The same 

 (in section) seen from the side, after removal of the anterior 

 half of the calyx. 3. Older flower seen from above. J, sepals ; 

 p, petals; a, anthers ; st^ stigma; ov^ ovary ; k, nectary. 



