146 TESTING OP SEEDS. 



tation and decomposition, excessive loss of moisture, and attacks of 

 insects. Hence before taking over or using seeds, they should be 

 thoroughly examined. 



There are three practical ways of testing the germinative power 

 of seeds ; they may be termed respectively (a) the ocular (b) the 

 weight and (c) the germination tests. 



Whichever method is employed, if the quantity to be tested is 

 very large, it should be divided into smaller lots and each such lot 

 should be examined separately. Moreover from each lot the seeds 

 should be taken, without any selection, from different points, a few 

 from each. 



A. The Ocular Test. 



This method of test, as the name implies, consists in the examina- 

 tion of the seeds with the eye, assisted, if necessary, with an or- 

 dinary magnifying lens. If the seed is sufficiently large, it is cut 

 in two with a sharp knife and the section is then examined. The 

 germ, including the perisperm (when there is any) should, if 

 thoroughly sound, fill the testa completely, possess the healthy 

 colour peculiar to the ripe seed of the species in question, emit no 

 unpleasant odour and contain a sufficient amount of moisture. 

 Next, the testa should be removed in order to assure oneself of the 

 soundness of the plumule and radicle. The size of the seed is no 

 criterion of its germinating power, but the larger seed generally 

 produces the hardier and more vigorus seedling. 



When the seeds are too small to be cut open easily, unless they 

 are oily, we have no proof of their soundess beyond the absence of 

 any unpleasant odour and the healthy appearence of the outside 

 of the testa. If they are oily, the presence of the oil is ascertained 

 by crushing them on a hard surface with the nail of the thumb or, 

 if very unyielding, with a hammer-head. A spot of oil or grease on 

 the nail or hammer-head will be a certain sign that they are good, 

 for in seeds that are at all decomposed, the oil will have dis- 

 appeared, having been oxidized and converted into other substances. 

 Sometimes small seeds are tested for moisture by placing them 

 on a red-hot iron plate. If the seeds burst with a slight explosion, 

 due to the sudden formation of steam, it is a proof that they contain 

 a sufficient amount of moisture. 



The ocular examination of seeds requires great experience and 

 special knowledge, and even then there is no sUght risk of error, 

 particularly in the case of small seeds. It ought never, if we can 

 help it, to be employed by itself as a final test in taking over any 

 large quantity of seed, and its use should, as a rule, be confined ta 



