NURSERY PRACTICE FOR PRAIRIE-PLAINS PLANTING 21 



air at temperatures sufficiently higher to effect approximately the 

 same rate of drying. A draft of air is somewhat cooling and affects 

 the seed more superficially than drying at high temperatures. 



Assuming the seed is to be put away somewhat moist, a temperature 

 below 40° F. is highly desirable, and in the early fall this almost 

 certainly requires cold storage. 



Where seed is certain to be used the following spring, and stratifica- 

 tion over winter is the easiest method for disposing of it, the tempera- 

 ture of the medium should be not higher than 50° F. at the start, 

 with prospect of early lower temperatures. In short, even with types 

 of seed which commonly require afterripening, a few seeds are likely 

 to germinate in the early period of stratification if the temperature is 

 50° or more. 



Cold storage in a moist atmosphere below 40° F. will fully care for 

 seed which sprouts readily in the fall even at moderately low tem- 

 peratures, and will equally well preserve elm seed. Also, even the 

 seed which is better off in a very dry condition will not deteriorate 

 appreciably in cold storage for some time. Cold storage can be de- 

 pended on to preserve stony seed which do not tolerate any serious 

 drying, and at the same time to "crack" them in readiness for ger- 

 mination. 



DRY STORAGE 



At the other extreme, it is well to consider what it is possible to do 

 with seed which tolerate a very dry condition. Lodgepole pine 

 seed, after being reasonably dried in the course of extraction, were 

 further dried in a stream of air at 170° F. for 4 hours without the 

 slightest injury and with actual improvement of keeping qualities, 

 according to the experiments of Bates (1). 



Other forms of severe drying have been used, holding pine seeds 

 in atmospheres of 20 to 40 percent relative humidity as long as any 

 loss of moisture was evident. Norway pine seed tolerated 20 percent 

 relative humidity, with a reduction of the moisture of the seed to 3 or 4 

 percent. White pine is probably injured by drying to that degree and 

 may be better preserved at 6 to 7 percent of its own weight in moisture. 



Red and white pine stand about 150° and 120° F., respectively, for 

 periods of 8 to 10 hours in the kiln without serious loss of viability. 



It seems probable that nearly all leguminous seed will tolerate at 

 least the degree of drying recommended for white pine. While these 

 seed appear to dry adequately in ordinary air as they ripen, and to 

 maintain vitality for years, experience to date indicates that more 

 perfect preservation can be attained through slightly greater drying 

 and sealed storage. 



If seed can be put away in sealed containers with very low moisture 

 contents such as indicated above, they may be kept for a long time at 

 any moderate temperature, or still better at low temperatures. A 

 desiccant such as calcium chloride or charcoal can be placed in the 

 can to reduce still further the moisture content of the seed. 



High temperatures, such as occur under room conditions or in 

 sheds in the summer, are dangerous to seed not entirely because they 

 induce increased respiration but also because they cause spoilage o( 

 fatty materials. Seed containing much food stored in the form of 

 fats and oils are especially susceptible to decomposition if exposed to 

 high temperatures for a considerable period. 



