PROPAGATION BY MEANS OF SEEDS AND SPORES 35 



The stratification of seeds 



Many seeds demand treatment preparatory to sowing. 

 Nearly all hard and bony seeds fail to germinate, or at least 

 germinate very irregularly, if their contents are allowed to 

 become thoroughly dry and hard. The shells must also be 

 softened or broken, in many cases, before the embryo can grow. 

 Nature treats such seeds by keeping them constantly moist 

 under leaves or mold, and by cracking them with frost. This 

 suggests the practice known to gardeners as stratification, an 

 operation that consists in mixing seeds with earth and exposing 

 them to frost or to moisture for a considerable time (cf. page 24). 



Stratification is practiced, as a rule, with all nuts, the seeds 

 of forest trees, shrubs, the pips of haws and often of roses, and 

 in many cases with the seeds of common fruits. 



Seeds should be stratified as soon as possible after they are 

 mature. Small seeds are usually placed in thin layers in a 

 box alternating with an inch or two of sand. Sometimes the 

 seeds are mixed indiscriminately in the sand, but unless they 

 are large it is troublesome to separate them at sowing-time. 

 The sand is often sown with the seeds, however, but it is diffi- 

 cult in such cases to distribute the seeds evenly, and in sowing 

 large quantities the handling of the sand entails a considerable 

 burden and becomes an item of expense. It is advisable to 

 pass the sand through a sieve of finer mesh than the seeds, and 

 the seeds can then be sifted out at sowing-time. If the seeds 

 are very small or few in number, they may be placed between 

 folds of thin muslin, which is then laid in the sand. Any 

 shallow box, like a gardener's "flat," is useful in making strati- 

 fications, or pots may be used with small lots of seeds although 

 pots are likely to be shattered by much freezing. A flat four 

 inches in depth might contain two or three layers or strata of 

 seeds the size of peas. 



The disposition of the boxes when filled varies with different 



