ALFALFA SEED PRODUCTION. 6 



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 Miiller ^ gave an extended description of the 

 aKalfa 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. MtiUer 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 imtripped flowers does occur, citing Hil- 

 debrand's work as confirmatory. Miiller 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 proboscis on one side of the untripped flower, which 

 under no circumstances results in tripping. 



1 Hildebrand, F. H. G. "Federigo Delpino's Beobachtungen liber die Bestaubungsvorrichtungen bei 

 den Phanerogamen. Botanische Zeitung, Jahrg. 25, No. 36, p. 283, 1867. 



2 Urban, I. Prodromus einer Monographie der Gattung Medicago L. Verhandlungen, Botanischer 

 Verein, Proviaz Brandenburg, Jahrg. 15, p. 13-16, 1873. 



' Miiller, Hermann. Die Befruchtung der Blumen durch Insekten und die gegenseitigen Anpassungen 

 beider. Leipzig, 1873, 478 p., 152 fig. 



