PLANT PROPAGATION 



37 



followed by decay if the water is warm enough for the organisms 

 of decay to multiply. 



Many seeds have such hard or tough seed coats that they 

 require treatment before being planted. This treatment permits 

 the water to enter so that the embryo may begin its growth. 

 Most hard seeds like nuts and the seeds of the peach may be 

 frozen by mixing or layering them with sand (Fig. 1 9) and leav- 

 ing them outdoors all winter in an open box, bedded in soil or 

 sand. This is called stratification. Many seeds which do not have 

 hard coats, such as the seeds of most forest trees and those 

 of many shrubs, are benefited by being stratified over winter, as 

 they are thus kept moist and soft. Seeds with rubbery coats 

 like the locusts and the coffee bean are benefited by being 

 stratified, but they are best 

 treated by soaking them in hot 

 water for a few hours just be- 

 fore planting, in order to dis- 

 solve the protective covering, 

 which is impervious to cold 

 water. In rare cases holes are 

 bored in such seeds as the 

 canna and the water chinquapin 

 to admit the moisture necessary for germination. In other cases 

 the outer coat has been dissolved with a mild acid like vinegar, 

 and sometimes even sulphuric acid is used with good effect. 

 Some such treatment may be used to secure quick germination 

 in clover, alfalfa, and cotton seed. 



41. How long do seeds remain alive? In every live seed 

 certain vital activities are thought to go on constantly, even in 

 ordinary storage. The enzymes which change the stored foods 

 into sugar are more active in some seeds than in others. These 

 activities result in lowering the vitality of the seeds. The vitality 

 of seeds is also affected by their maturity and by the -conditions 

 under which they are harvested and stored. Seeds that are 

 harvested before they are ripe lose their vitality in a much 

 shorter time than those that are harvested when mature. Also 



FIG. 19. Device for treating heavy- 

 walled seeds 



The seeds are layered or stratified in the 

 sand and left out of doors during winter 



