partrun] § THE MECHANISMS OF FLOWERS. 175 
F 
_ We must, therefore, take young flowers, to see the squeezing 
out of the pollen. Thus the flowers of Ononis afford a stage inter- 
mediate between Lotus with its piston-mechanism, and Melilotus in 
which the reproductive organs simply emerge from the carina. 
In regard to the formation of the “piston,” Ononis stands 
between Lotus and Anthyllis. In Lotus the five outer filaments, 
which alternate with the petals, are thickened at their ends to 
express the pollen; in Anthyllis the ends of the filaments are all 
_ thickened alike ; in Ononis they are all thickened, but the outer 
whorl much more so than the inner. While the outer stamens thus 
perform the function of a piston to a greater extent than the inner, 
' the inner (1b) produce pollen in much larger amount than the outer 
(la). This is an interesting step towards separation of the two 
_ whorls of stamens for two distinct purposes. 
i Though the flowers of Ononis possess no honey they are visited 
_ by numerous bees, but in the number of their visitors they are far 
behind Lotus, which has abundant honey. It is curious that not only 
female bees but males also often visit several flowers in succession 
-and perform all the actions of sucking. They have obviously no 
outward token of the lack of honey, but must discover it by 
experience. The females, after making sure that there is no honey, 
take to collecting pollen ; the males, on the other hand, abandon the 
' flowers after a few vain attempts, though they may remain some 
time about the plant in pursuit of the female. The visitors are ex- 
usively bees, and mainly forms with abdominal collecting-brushes, 
A. Bees with abdominal collecting-brushes : (1) Osmia aurulenta, Pz. 9 
(Thur.), ab. ; (2) O. wenea L. 9, freq. ; (3) Megachile versicolor, Sm. (Haar) ; 
(4) M. pyrina, Lep. 2 ¢, freq.; (5) M. circumcincta, K. 9, ab. ; (6) M 
maritima, K. 9; (7) Anthidium manicatum, L. 2 g, ab.; (8) A. punctatum, 
tr. 2 ¢; (b) Bees with tibial pollen-baskets: (9) Apis mellifica, L. § ; (10) 
- Cilissa leporina, Pz. 2 ; (11) Anthophora quadrimaculata, Pz. 9 ¢, ab. (Thur.) ; 
_ (12) Bombus lapidarius, L. §; (13) B. terrestris, L. 9. 
a 
; Ononis repens, L., is also visited exclusively by bees (590, II. 
ip. 254). 
r According to Bentham, most species of Ononis in southern 
Europe are liable to abortion of the corolla in spring, and cleisto- 
_gamic self-fertilisation then takes place (399, p. 67; 531, p. 312). 
Parochetus, Ham., has eptogemic flowers, according to Kuhn. 
93, MEDICAGO SATIVA, eelay Wee as the mechanism of this 
flower has been several times the subject of careful study, it is by 
