| ALFALFA SEED PRODUCTION. 3 
curvature is due to the contraction of the cells on the upper side or 
the distension of those on the convex side. After the explosion of 
the flower he states that the tube can not be straightened to its 
original position without causing a transverse fracture. No simi- 
lar elasticity was found in the free filament or in the pistil, but the 
tendency of the keel to open laterally was noted. Henslow also 
observed honeybees gathering nectar from alfalfa flowers, but in no 
instance observed by him was the bee able to trip the flower. He 
also mentions that he did not see bumblebees visiting the flowers. 
These observations were made in England. 
In the same year Delpino described the structure and mechanism 
of the alfalfa flower. He apparently considered the explosive force 
due to the irritability of the stamineal tube. Hildebrand! criticizes 
this conclusion and points out that the explosion is due to the ten- 
sion of the upper filaments in the stamineal tube. He agrees, how- 
ever, that, after tripping, insects are barred from reaching the nectary. 
Urban,” in 1873, refers to some of the preceding literature and 
gives a detailed description of the corolla and of the explosive mech- 
anism. According to his observations, only bees bring about pol- 
lination, although butterflies are frequent visitors. In rare cases 
untripped flowers were found to form pods and seeds. Shortly after 
the flower has been tripped the opening to the nectary is closed by 
the drooping of the edges of the standard. 
In the same year Milier* gave an extended description of the 
alfalfa flower, together with excellent figures, in which the whole 
mechanism is clearly explained. The elastic tension of the stamineal 
column is mainly in the upper stamens, as can be determined by 
dividing the upper ones from the lower. The former then show 
much greater curvature. Miller gives a considerable list of insects, 
including the honeybee and numerous butterflies, which he had 
_ observed sucking nectar from the flowers, but states that he never 
succeeded in seeing the explosion of the flower actually performed 
by insects, though he watched for it frequently. He also states 
that self-pollination in untripped flowers does occur, citing Hil- 
debrand’s work as confirmatory. Miller also calls attention to 
certain imperfections of the mechanism of the flower, namely, that 
nectar secretion continues to take place after the flower is exploded, 
thus continuing to attract insects without obtaining any additional 
benefit, and, second, that bees and butterflies can obtain the nectar 
by inserting the ast eee on one side of the untripped flower, we 
- under no circumstances results in tripping. 
1 Hildebrand, F. H. G. Federigo Delpino’s Beobachtungen iiber die Bestiubungsvorrichtungen bei 
den Phanerogamen. Botanische Zeitung, Jahrg. 25, No. 36, p. 283, 1867. 
2Urban, I. Prodromus einer Monographie der Gattung Medicago L. Verhandlungen, Botanischer 
Verein, Provinz Brandenburg, Jahrg. 15, p. 13-16, 1873. 
3’ Muller, Hermann. Die Befruchtung der Blumen durch Insekten und die gegenseitigen Anpassungen 
beider. Leipzig, 1873, 478 p., 152 fig. 
