PLANT REPRODUCTION 157 



and dried. The seeds which are liberated are then col- 

 lected and sold. Some are mature but many are valueless. 

 Often seeds may have been frosted while yet immature or 

 before they have dried sufficiently, and this renders them 

 liable to low germinating power. They may have been 

 damp when gathered, and consequently subjected to 

 heating later, or they may have been attacked by 

 insects. 



It is not necessary 7 to sow seeds in soil in order to test 

 their germinating power. A simple seed tester consists 

 of two circular pieces of clean cotton flannel, a plate 

 and a pane of glass. The cloths are dipped in water, and 

 squeezed a few times while under water to press out the 

 air. They are then left moderately wet and one is spread 

 over the bottom of the plate. The seeds to be tested are 

 placed on this cloth and covered with the other. The plate 

 and cloths are next covered with the pane of glass to check 

 the evaporation, and then placed in a temperature re- 

 quired by the species. The seeds should be examined 

 frequently and removed as they sprout. A definite 

 number should be tested so the percentage of viable seeds 

 may be determined . The cloth should be boiled before using 

 a second time, in order to destroy any molds which might 

 develop and interfere with the germination of other seeds. 

 There are several elaborate seed testers but the arrange- 

 ment described, serves for most seeds. 



120. Time required for germination. The time re- 

 quired for germination varies greatly in different species 

 of plants, and there is also a great variation even in seeds 

 of the same species and variety. In primroses and petu- 

 nias, for example, many of the choicest colors will not ger- 

 minate until long after the less attractive colors have pro- 

 duced strong seedlings. For this reason, it is better not 



