CAUSES OF LOSSES IN VITALITY. 



23 



temperature increases, but the injury due to the increase in tempera- 

 ture is dependent on the amount of moisture present. 



The following table lias been compiled in order to show the ratio 

 between the loss in vitality and the precipitation and temperature. 

 The loss in vitality, as given in the second column of Table VII, rep- 

 resents the average losses in percentages, calculated from the results 

 of the germination tests of the 13 different samples of seeds, as shown 

 in Table II." 



The third column shows the annual precipitation in inches. The 

 annual precipitation has been taken, because in some instances heavy 

 rainfalls occurred just previous to the time that the seeds were put 

 into storage. Then, too, the annual precipitation furnishes more accu- 

 rate data for a basis of comparison. The mean temperatures, as given 

 in column 4, are not the mean annual temperatures, but the averages 

 covering the time during which the seeds were stored. The mean 

 annual temperatures were not taken, chiefly for the reason that the 

 critical period, in so far as temperature is concerned, is during the 

 summer months. 



TABLE VII. Ratio between vitality, precipitation, and temperature. & 



"These seeds were sent out in February, 1900, and were returned to the botanical laboratory and 

 tested in October and November, 1900. The average time that the seeds were kept at the various 

 places was 252 days. 



?> The results of the San Juan tests have been omitted from this table because, as has been previously 

 stated, all of the seeds were returned from San Juan on June 20, 1900, when the first tests were made. 

 The second series of tests was made in October, 1900. During the time intervening between the first 

 and second tests the San Juan samples were kept in the botanical laboratory at the University of 

 Michigan. 



According to the table the seeds kept at Mobile suffered the greatest loss in vitality. However, it is 

 quite probable that the greatest loss would have been from the seeds stored at San Juan had the time 

 of storage been the same for the two places, so that the results of the San Juan tests could have been 

 included in the table. This conclusion is based on the following facts: Normally, the number of rainy 

 days at San Juan far exceeds those at Mobile. In 1900 there were 211 days on which rain fell in San 

 Juan, while the records for Mobile show only 146. Likewise the average temperature of the dew-point 

 Tor San Juan was 71 F. and only 59 F. for Mobile, which, when expressed in terms of absolute 

 moisture, gives s.iMO and 5.555 grains of water per cubic foot at the time of saturation. On the other 

 hand, the relative humidity of San Juan was 78.5 per cent, or slightly lower than that of Mobile, the 

 latter having a relative humidity of 80.5 per cent. However, the mean annual temperatures were 

 77.G and 71.4 F., respectively, hence a mean absolute humidity of 7.099 grains of aqueous vapor for 

 San Juan and only 6.718 grains per cubic foot for Mobile. 



