RUTACEAE 241 



of them. After the pollen has been shed, the filaments straighten, and the style 

 with the mature stigma bends upwards at right angles, so that a female condition 

 ensues. An insect with proboscis of suitable length probing for the nectar secreted 

 in the base of the flower, must therefore introduce its tongue between the petals 

 and the stamens, or stigma, so that when flowers of different ages are visited, cross- 

 pollination necessarily takes place. 



Visitors. In the Kiel Botanic Garden, I observed the following three bees, all 

 freq., skg.: 1. Megachile willughbiella K. 5 and $; 2. Bombus lapidarius L. jjl; 

 3. Apis mellifica L. |jj. Of these visitors, however, the honey-bee alone regularly 

 alighted in such a way as to touch the anthers or the stigma, and so constantly 

 effected cross-pollination, the two others often approached laterally, so that they 

 only touched the filaments. 



Loew saw two bees in the Berlin Botanic Garden : 1. Apis mellifica Z. Jjj, skg. 

 and po-cltg. ; 2. Bombus agrorum F. 5 and $f, do. On the variety roseus he saw two 

 others: 1. Megachile centuncularis Z. 5, po-cltg., hovering above the anthers and 

 removing pollen with its ventral brush ; 2. M. circumcincta K. $, skg. 



2. Tribe Boronieae. 



179. Correa Andr. 



Flowers protandrous (Delpino, 'Ult. oss./ p. 170). Numerous species have been 

 studied in the Berlin Botanic Garden by Urban with regard to pollination (cf. abstract 

 of his paper in Bot. Centralbl., Cassel, xiv, 1883, pp. 200-4). 



3. Tribe Toddalieae. 



180. Ptelea L. 



Flowers greenish, pseudo-hermaphrodite, dioecious, in pseudo-umbellate racemes; 

 with concealed nectar secreted in their bases. 



607. P. trifoliata L. (Knuth, ' Bloemenbiol. Bijdragen.') This North 

 American shrub is occasionally cultivated in our gardens. The whitish-green flowers 

 exhale a strong odour of hyacinths; they secrete a very small quantity of nectar 

 below the ovary, by which it is concealed in the female flower, and in the male 

 flower by the staminal hairs as well. The female flower possesses vestigial stamens, 

 the anthers of which are sterile ; the terminal stigma projects 1-2 mm. beyond them. 

 The male flower possesses a moderately large ovary, but this develops no further. 

 The five stamens are closely beset with white hairs of moderate length on the 

 inner side of the lower halves of their filaments. These hairs serve to protect 

 the nectar from rain, and keep off unbidden guests. The anthers dehisce simul- 

 taneously, and turn their pollen-covered sides upwards, so that a nectar-seeking 

 insect dusts its head or thorax with a ring of pollen, and when it visits a female 

 flower, this must be applied to the stigma. The male flowers are considerably 



