38 THE SEED AND ITS NEEDS 



Germinative Energy of a Seed. — ^The germinative energy 

 or the speed of germination is that energy which is re- 

 quired for the germination of a seed. The length of time 

 this energy is available varies from a few hours to several 

 years, depending upon the different species of plants. The 

 reasons for these variations in certain plants are not well 

 understood, although they are probably caused to some 

 extent (1) by the different degrees of ripeness of the seed, 

 (2) by the nature of the seed coat, and (3) by the differ- 

 ent degrees of stability of the food compounds. Possibly, 

 the embryo might be influenced to a limited extent by 

 heredity. 



The shorter the period of germination the better, because 

 after the seed is once planted it is in constant danger of 

 destruction from various causes, as for example by insects or 

 predaceous animals. 



The seed of different species of plants require different 

 germinative periods, but there is an abnormal condition 

 recognized by seedsmen due to the hard condition of the 

 testa or seed coat of some seed, and because of this hardness 

 of the seed coat the absorption of water cannot take place. 

 These seed are known as "hard seed," or hard-shelled seed, 

 and are common in legumes as well as in some other plants. 

 The power to germinate is present in these hard-coated seeds, 

 and their value is not impaired. This defect is caused for the 

 most part by the presence of abnormal quantities of silica, 

 lime and other ash ingredients in the seed coat, and are 

 substances which are not affected by soaking in water. 

 These defects can be remedied (1) by filing of the seed coat, 

 (2) by mixing the seed with sharp sand, (3) by revolving the 

 seed in a cylinder with corrugated edge, (4) by the cracking 

 or the breaking of the seed coat with a hammer, (5) by the 

 treatment of the seed with chemicals such as weak acids. 



Seed Testing. — In order to guard against failure, germi- 

 nation tests for all seed should be made everj;^ season. Seed 

 testing consists in the counting out of a definite number of 

 seed, of which the usual number is one hundred. The seed 

 must not be specially selected, but should represent a fair 

 sample of the lot. 



