420 GENETICS IN RELATION TO AGRICULTURE 



Planting pedigree cultures involves some of the most difficult prob- 

 lems especially in handling small seeds. Larger seeds such as wheat, 

 corn, peas and beans are handled satisfactorily by planting a single seed 

 in a paper planting pot containing thoroughly sifted soil. If more than 

 one seedling of the species planted should appear in a single pot, it should 

 be discarded. These individual plants should then be set out at equi- 

 distant points in the rows and each row labeled. Also at the time of 

 planting a memorandum should be made of the plan of the plot with the 

 position or number and contents of each row as a safeguard in case of loss 

 of labels. Small seeds like tobacco, petunia, primula and even those like 

 the strawberry should be planted in sterilized soil in order that any seeds 

 of the same species that happen to be in the soil will be destroyed. The 

 most satisfactory method of sterilizing soil for seedage is to steam it under 

 pressure. The soil is placed in the clean earthenware pots or seed pans, 

 in which the seeds are to be sown, and these go directly into the auto- 

 clave, where they should remain under pressure of 15 pounds to the square 

 inch for at least 1 hour. Where gas is not available for heating the 

 autoclave an alcohol blast lamp may be used. If it is not convenient to 

 prepare the sterilized soil fresh each day as needed, the pots not intended 

 for immediate use should be covered before being sterilized with a piece of 

 fine-meshed fabric which is securely tied below the flange of the pot. This 

 covering is left in place until the pot is used. The manipulator should have 

 clean hands, clothes and utensils and should handle only one lot of seed 

 at a time using due precaution between each lot to avoid mixing. Each 

 lot should be labeled as soon as sown. The seed pots or pans are then 

 moistened by setting them in a vessel containing water, care being 

 taken not to let the water overflow into the seed vessels. All subsequent 

 watering should be by means of sub-irrigation rather than surface 

 watering when dealing with small seeds, or if this is not practicable the 

 water used in sprinkling should be filtered or strained. When ready to 

 prick out, the little seedlings may be transplanted into unsterilized soil 

 provided they are set at uniform distances so that any foreign seedlings 

 that appear later can be distinguished with certainty. This is easily 

 accomplished by selecting a board the same size as the flat and ruling it 

 into squares, then driving tenpenny nails through the corners of the 

 squares. With this tool the holes are made for a whole flat of seedlings 

 at once and they are uniformly spaced. If the seedlings are minute it is 

 a wise precaution to mark each as it is pricked out by sticking a tooth 

 pick into the soil close to it. 



Protection of cultures also involves problems which are highly impor- 

 tant in pedigree plant breeding but difficult to discuss without entering 

 into considerable detail. The danger may appear in the form of curious 

 or ignorant persons who do not understand the importance of keeping 



