22 MISC. PUBLICATION 434, U. S. DEPARTMENT OF AGRICULTURE 



Cellars in which temperatures do not vary greatly between winter 

 and summer, or at least do not reach a high point in summer, would be 

 reasonably satisfactory for maintaining the vitality of seed, were it 

 not that humidity is usually quite high in cellars. It is useless to dry 

 seed to an equivalent of 30 to 40 percent relative humidity if they 

 are later to be exposed in the slightest degree to humid atmosphere. 

 Sealed containers are essential, but that term can hardly be applied 

 with propriety to anything except metal cans with all seams soldered, 

 or glass jars or bottles with ground stoppers. Neither corks nor 

 rubber gaskets can be fully depended on to exclude atmospheric 

 moisture, which dry seed will absorb with great avidity if there is any 

 leakage whatever. 



Summarizing, for seed which can be thoroughly dried and which 

 it is necessary and desirable to store for periods of 1 to several years: 



1. Storage in sealed containers at low temperatures of 33° to 40° F. 

 after full drying is most desirable. Somewhat higher temperatures 

 are not harmful but are not as desirable. 



2. If sealed containers cannot be employed, the constant low 

 temperatures of a cold-storage plant offer best protection despite 

 fairly high humidity. Ice-cooled plants are likely to be too moist. 



3. If neither containers nor cold storage can be had, a well- venti- 

 lated, thoroughly dry building should be used. High temperatures 

 occurring in poorly ventilated lofts or attics should be avoided. A 

 north, second-story room, sealed off from the roof, is best. 



4. Fatty seed, such as most pines and many nuts, should not be 

 exposed to temperatures above 80° F. 



Treatments to Stimulate Germination 



Nurserymen in the prairie-plains region have definitely come to 

 the conclusion that any seed treatment that will shorten the germinat- 

 ing period after sowing is helpful, since this period is the most critical 

 of the entire nursery season. The shorter it can be made, the less 

 danger there will be of losses from heat, damping-off, drying, crust 

 formation, and other ills that beset the seedling during the germinating 

 period. An additional advantage of a short germination period is 

 that the stock produced is of a more uniform size and fewer cull 

 seedlings result. Furthermore, the proper treatment of the seed will 

 give a much higher percent of germination. 



THE PROBLEM OF SEED DORMANCY 



Any difficulty arising from the need for afterripening or pregermina- 

 tion treatment of seed is most readily overcome by fall sowing, when 

 this is feasible and when it is known the seed will not spoil or become 

 active before cold weather. As has already been indicated, for seed 

 which are known to require a long exposure to moisture, including the 

 afterripening period, stratification over winter is best, or at least next 

 best to fall sowing in the nursery. 



It is very difficult to draw a sharp line between processes which 

 have already been referred to as afterripening, or completion of the 

 ripening process, and those which are necessary as a preliminary to 

 germination and which, in the artificial handling of seed, are referred 

 to as pregermination treatment. The one sort merges into the other, 



