110 SEEDING AND PLANTING 



18. THE DETERMINATION OF VIABILITY BY DIRECT INSPECTION 



The method of judging viability by direct inspection is as fol- 

 lows: A sample of 100 or 200 seeds is selected from those to be 

 examined, care being exercised that the sample is an average of 

 the entire lot. Accuracy in the selection of the sample can be 

 attained by thoroughly mixing the seed and placing a quantity of 

 it upon a smooth, flat surface in a cone-shaped pile. The pile is 

 then flattened out in circular form until its thickness is but two 

 to five times the greatest diameter of the seed. It is then divided 

 into quarters and one of the quarters selected and divided by the 

 same method as before. This process is continued until the sample 

 with its impurities is reduced to the approximate number of seed 

 required. The seeds in this sample which represent an average 

 of the entire lot are taken one at a time and carefully examined. 

 A good lens and a sharp knife are essential in making this exami- 

 nation. The viable seeds are among those in which the kernel 

 is firm, plump, and sweet-smelling. The blind, wormy, rancid, 

 moldy, shriveled, and otherwise damaged ones are dead. The 

 estimate of viability is the per cent of the former to the whole 

 number examined. 



19. Evidences of Viability from the External Appearance of 

 the Seed. The examination of the exterior of the seed seldom 

 presents satisfactory evidence of viability. The investigations of 

 Schwappach show that the black seeds of Scotch pine have a 

 higher germination than the lighter colored ones. In coniferous 

 species the outer appearance of the seed coats should be clear 

 and bright. A wrinkled seed coat indicates that the seed is over- 

 dry. A cracked seed coat, so long as the kernel is uninjured, 

 does not necessarily imply loss of viability. 



20. Evidences of Viability from the Internal Appearance of 

 the Seed. As a rule, the interior of the seed is white although 

 there are a number of exceptions. Thus the endosperm and em- 

 bryo of the seed of most pines are yellow. In the maple the 

 embryo is green. Spots in the endosperm or embryo, abnormal 

 softness, rancidness, and other characteristics which are not con- 

 stant or characteristic of normal development indicate loss in 

 viability. All seeds in which the kernel has failed to develop 

 are "blind." A withered or hard embryo or endosperm usually 

 indicates overdrying. The endosperm in old seed gradually loses 



