20 MISC. PUBLICATION 4 3 4, U. S. DEPARTMENT OF AGRICULTURE 



life processes. In brief, seed vary in the degree to which they can be 

 put to sleep. Insofar as this condition is caused by drying, it should 

 be referred to as induced dormancy. In many cases this causes 

 changes which are difficult to reverse. 



The seed of green ash, for example, is certainly mature enough by 

 the time it becomes reasonably dry on the tree and will germinate in 

 a relatively short time if placed in w-arm, moist soil. Although the 

 species does have some embryo dormancy, it does not have it in the 

 degree that junipers and similar species have. Yet, if seed of green 

 ash is stored for several years and becomes quite dry, the seed coat 

 becomes so impervious to moisture as to require water-soaking for 

 about 2 weeks before it will germinate. But it wall then germinate 

 only slightly less freely than the fresh seed. Thus, dormancy may be 

 induced to the point where revival becomes a matter of some difficulty 

 and yet after at least 3 or 4 years of such dormancy the seed suffers no 

 serious loss in viability. 



The more sensitive types of seed that require storage over winter 

 can withstand little induced dormancy. They must be stored in the 

 presence of some moisture and with temperatures below T 40° F., and 

 the dormancy they undergo, insofar as it differs from the inherent 

 dormancy discussed later, corresponds with the winter dormancy of 

 all kinds of woody plants and of the roots of perennials, in which 

 severe drying of the tissues is likely to be fatal. It is not known how 

 long this type of dormancy can be maintained in seed, but probably 

 not more than a few months, since even at 40°, with ample moisture, 

 respiration will proceed at a moderate rate. 



Afterripening is not quite the same process in different types of 

 seed. Some seed are ready to germinate as soon as they have com- 

 pleted their growth and usually have exchanged their green coloring 

 matter for something of a ruddy hue. Others will not be ready for 

 many months, and it is unquestioned that during this period certain 

 chemical changes occur which represent a continuation of the ripening 

 process. These changes are accompanied by the slow exclusion or 

 occlusion of moisture, the latter implying that the moisture is used 

 and combined within the seed. They may or may not depend on the 

 gradual lowering of temperatures in the autumn. 



The first practical bearing of these facts is that the afterripening of 

 seed may be prevented and the seed germination at a later date made 

 slower or more difficult if artificial drying is too severe or applied too 

 soon after picking. Second, seed put away early, which may still be 

 under compulsion to sw T eat out some moisture, if kept in a poorly 

 ventilated mass at temperatures above 40° F., may be subject to 

 molding and heating. It WT>uld hardly be possible to overemphasize 

 the desirability of maintaining the natural routine of seed ripening as 

 closely as possible when handling and storing seed in large quantities. 



COLD STORAGE 



All of the above considerations lead to the following precautions 

 and procedures to be employed wherever there is any question as to 

 just what degree of treatment a given kind of seed will tolerate without 

 injury: 



Do not dry seed too fast, too long, or at high temperatures. Drying 

 under a current of moderately warm air is safer than drying in still 



