350 GENETICS IN RELATION TO AGRICULTURE 
ful crosses.”” The various implements mentioned above are shown in 
Fig. 147. 
Some of the Difficulties Attending Hybridization —(a) Dvzfferent 
Seasons of Maturity—This is a common obstacle to the crossing of 
different forms. When it involves merely growing periods of unequal 
length the difficulty can be overcome easily by planting at such times 
that the various forms will flower simultaneously. When this is not 
feasible it becomes necessary to resort to some method of preserving the 
pollen. It has been found that pollen of certain species will retain 
vitality for weeks or even months if it is kept very dry. Miss Kellerman 
Fie. 147.—Implements used in castrating and depollinating hermaphrodite flowers. 
Right, self-closing forceps, ordinary forceps, scissors and scalpel. Left, chip blowers and 
syringes. (Courtesy U. S. Department of Agriculture.) 
reports that the most effective method tried by the Bureau of Plant 
Industry was as follows: anthers were placed in dried vacuum glass tubes, 
e.g., tube filled with anthers 1—2 inches, cotton 1¢ inch, exhausted to about 
0.5 mm. pressure in the presence of sulfuric acid, the tube then sealed. 
As far as practicable the pollen was kept at a temperature of 10°C. A 
simpler and very useful method is to make a double container by fitting 
a small vial inside a larger one and partially filling the space between the 
two with anhydrous calcium chloride or sulfuric acid, filling in the 
upper portion with absorbent cotton and tightly corking the larger 
vial. The anthers or pollen grains are placed in the inner vial after it 
has been thoroughly sterilized and allowed to dry. 
(b) Failure of Fertilization —This may be due to many causes ranging 
from simple morphological maladjustments to complex physiological 
relations amounting to antagonism. Probably a very frequent cause of 
unsuccessful crosses is failure of the pollen to germinate. When repeated 
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