April, 192 



SCIENTIFIC AGRICULTURK. 



259 



Stamens. — Tliere are ten stamens, the 

 filaments of nine being fused together to 

 form a hollow tube-like structure which 

 may be ternunl the staminal tube. At 

 the upper end of the tube the ends of the 

 filaments are free, the anthers being at- 

 tached to the free ends. The filament of 

 the tenth stamen is quite detached and 

 free from the other nine and is situated 

 above the staminal tube, (ffsc.) 



Pistil. — Tlie pistil consists of style and 

 stigma and is contained in the staminal 

 tube. The style being nearly eq'ual in 

 length to the tube, the stigma is brought 

 into a position slightly below that of the 

 anthers: this appears to favor the chances 

 of the flower being self-pollinated. 



The staminal tube together with the en- 

 closed pistil may be conveniently referred 

 to as the sexual column. This column is 

 completely inclosed in the boat-shaped 

 structure formed by the two keel petals 

 and usually remains imprisoned in the 

 keel until liberated by wild bees or some 

 other suitable external agency. This act 

 of setting free the stamens and pistil is 

 commonly known as tripping the flower. 



Natural Tripping of the Alfalfa Flower. 



Tripping under natural conditions in 

 the field is usually brought about by wild 

 bees. Bees of the Megaohile species seem 

 to be most effective in tripping the flow- 

 ers. The hairs on the legs and abdomen 

 of these bees seem to be specially designed 

 to catch and to hold the pollen, and these 

 bees are frequently found with the under 

 part of the abdomen and thorax as well as 

 the upper parts of the legs completely 

 loaded up with masses of pollen; thus it 

 will be seen that this species of bee is a 

 very useful agent in the distribution of 

 pollen and in this way natural cross-polli- 

 nation of the Alfalfa flowers is usually 

 brought about. 



Honey bees visit the flowers regularly 

 in large numbers; but after extended ob- 

 servation over a number of years, the 

 writer has never yet seen a honey bee trip 

 an Alfalfa flower in the open under 

 natural conditions. This species of bee 

 seems to visit the Alfalfa flower for the 

 nectar alone and is able to extract this 

 from the keel without displacement of the 

 petals: moreover, the honey bee seems 



carefully to avoid tripping the flower. 

 Tripping the Alfalfa Flower by Hand. 



We do not purpose giving a detailed 

 account of the mechanism of the Alfalfa 

 flower, which causes tripping to take 

 place. A detailed account by Piper will 

 be found in (3: p, 7-9). It will, however, 

 be necessary to give a general account of 

 the M-ay the flower behaves under partic- 

 ular treatment. 



If some small object as a toothpick or 

 the point of a lead pencil is inserted be- 

 tween the upper edges of the keel petals, 

 they are forced slightly apart and the 

 sexual column rises up with spring-like 

 rapidity so that the stamens together with 

 the stigma strike the standard with con- 

 siderable force. The same result may be 

 obtained by simply pressing down on the 

 base of the keel with a pin or a piece of 

 grass stem. When the apex of the sexual 

 column rises up suddenly: the staminal 

 tube, acting like a released spring, curves 

 upward and the anthers together with the 

 stigma are brought against the face of the 

 standard with considerable force. 



The anthers being carried somewhat in 

 advance of the stigma are first to strike 

 the standard: this becomes dusted with 

 the poUen from the bursting pollen sacs. 

 The stigma, following immediately behind 

 the anthers, is brought against the stand- 

 ard with considerable force, the impact 

 being sufficiently strong as to cause the 

 pollen grains to become firmly attached 

 to the soft tissue of the stigma, thus 

 rendering self-pollination of the flower 

 practically certain. 



At this stage, an interesting question 

 arises as to whether the spring-like force 

 exerted by the sexual column is due to the 

 action of stamens or style. After repeated 

 failures to solve this problem, a method 

 of operating on the flower, which led to 

 the solution of the difficulty was hit 

 upon quite by accident. 



The experiment may be carried out as 

 follows: — Select a mature, well-formed, 

 untripped flower. After tripping, care- 

 fully slit open the staminal tube, taking 

 care not to injure the inclosed pistil. This 

 operation may readily be performed by 

 inserting the point of a dissecting needle 

 into the base of the tube and working it 



