ERICACEAE 



529. Rhododendron L. 



47 



Protandrous humble-bee flowers, usually brightly coloured ; nectar secreted by 

 an annular swelling at the base of the ovary. Kerner states that in many species the 

 pollen-tetrads are bound together by threads of viscin. 



1773. R. ferrugineum L. (Ricca, Atti Soc. ital. sc. nat., Milano, xiii ; Herm. 

 Muller, ' Alpenblumen/ pp. 378-9.) In this species the abundant nectar collects in 

 the base of the almost horizontal corolla-tube, especially in a slight pouch on the 

 upper side of this. The erect hairs on the filaments serve as nectar-covers. In 



Fig. 229. Rhododendron, L. (after Herm. Muller). A. A just-opened flower of/?, ferrugineum, L. 

 (natural size). B. A rather older flower of the same species. C. A young flower of R. hirsutiiin, L. 

 (in the male stage), after removal of the perianth and some of the stamens (x 7). D. An older flower 

 of the same species (in the female stage), treated similarly ( x 7). A, nectar ; w, nectary ; st, stigma. 



order to get at the nectar-bees and humble-bees must creep over the stamens 

 and stigma into the base of the flower, and if this is in the first stage their under-side 

 is dusted with pollen, which will be transferred to the stigmas of flowers in the second 

 stage. As the longest stamens project beyond the stigma, automatic self-pollination 

 is possible if insect-visits fail. 



Visitors. The following were recorded by the observers, and for the localities 

 stated. 



Herm. Muller (Alps), the honey-bee and 7 humble-bees, skg. legitimately and 

 eff"ecting cross-pollination ; also, as unbidden guests, a beetle, 4 flies, an ant, and 

 9 Lepidoptera. Ricca (Alps), humble-bees up to a height of 2,200 m. MacLeod 

 (Pyrenees), 3 humble-bees, Halictus, and a Muscid (Bot. Jaarb. Dodonaea, Ghent, iii, 

 1891, P- 373)- 



1774. R. hirsutum L. (Herm. IMUller, op. cit.) Hermann Muller says that 

 the flower mechanism of this species completely agrees with that of R. ferrugineum. 

 Hansgirg noticed the occurrence of pseudo-cleistogamy. 



