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 
Fic. 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; EH, 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- 
Digitized by Microsoft® 
