HYBRIDIZATION 



349 



the flower and lay aside ready for application to the stigmas of the flowers 

 which are to be depollinated. Second, select a raceme in which the 

 terminal buds are about to expand and cut away all the buds and flowers 

 except three or four near the center of the raceme. The flowers should 

 not be mutilated in any way and should be handled as little as possible. 

 In these flowers the stamens will have dehisced perhaps a day or two 

 previously but the pollen cannot reach the stigma until the flower is 

 tripped. When the tripping is uncontrolled the sexual column (pistil 

 and stamens) flies upward and strikes the banner with considerable force 



FIG. 146. Flowers of alfalfa (enlarged 4 diameters) showing method of depollinating 

 and crossing: A, untripped and unpollinated ; B, tripped and self-pollinated; C, tripped 

 against a pin to prevent self-pollination and permit depollination; D, after depollination 

 with water jet; E, after artificial pollination; F, after withdrawal of pin the stigma presses 

 against the surface of the banner. (After Oliver.) 



and pollen grains are imbedded on the receptive stigmatic surface. It is 

 necessary therefore to trip the flower gently and to prevent the stigma 

 from touching the banner which is accomplished by inserting a short pin 

 between the sexual column and the banner (see Fig. 146, C). Third, 

 depollination is accomplished by the use of a fine jet of water from a 

 dental chip blower; "the jet may be of sufficient force to remove even the 

 empty anthers without injury to the stigma." Then remove the water 

 adhering to the flower with a piece of clean, soft blotting paper. Fourth, 

 apply the waiting pollen to the depollinated stigma and gently remove 

 the pin allowing the stigma to press against the banner (Fig. 146, F). 

 "The operation is performed in much less time than it takes to describe 

 it and the operator is rewarded by a fairly high percentage of success- 



