LIFE SPAN OF SEEDS 



53 



winter months in the heated laboratory the water content was low. During 

 the moist, hot weather of summer the water content was high, reaching a 

 maximum in August when the water content was about twice that of the 

 winter months. It is also evident that different kinds of seeds vary con- 

 siderably in their water content when stored under identical atmospheric 

 conditions. Seeds in which the storage substances are mainly fats absorb 



Lettuce 



FEB. 1939 



MAY 



JULY AUG. SEPT. 



NOV. DEC. JAN. 1940 



Figure 17. Moisture contents at various times of the year of seeds stored open in the 

 laboratory. Moisture expressed as percentage of dry weight of seeds. 



ess water than those in which the storage substances are mainly carbol- 

 hydrates. Peanut and pine seeds are high in fats, tomato seeds low, and 

 flax seeds intermediate. No complete analyses for onion and lettuce seeds 

 are available, but microchemical tests show them rich in fats. None of 

 these six kinds of seeds bear carbohydrates as the main storage material. 

 All store their foods mainly in the form of proteins and fats. The nature 

 and thickness and chemical nature of the coats and other factors modify 

 the amount of water absorbed. The pine seeds absorb a higher percentage 

 of water than lettuce, although both are fatty seeds. Barton ^ has shown 

 not only that is high moisture content injurious to the keeping quality of 

 seeds but that fluctuation in moisture content is also detrimental. Fig. 17 

 shows the mde variation in water content in open storage. This is avoided 

 by sealed storage or by hard-coated seeds. 



Another interesting observation made by Barton ^ is the fact that with 

 different temperatures under the same relative humidities the amount of 

 moisture held by the seeds varies. Fig. 18 shows this variation. This is 

 especially marked at the higher humidities, 76 per cent and 55 per cent, 



