172 



STUDIES IN SEEDS AND FRUITS 



The maxi- 

 mum of the 

 hygroscopic 

 capacity. 



Nobbe's 

 experiments. 



And now we have to inquire into the nature of this extreme 

 limit of a seed's hygroscopicity. This is a difficult matter and 

 one concerning which awkward questions are likely to be raised. 

 In my own experiments the object was to ascertain the hygro- 

 scopic range of seeds during a fortnight of changeable weather ; 

 and the results procured, as shown in the table, differ but little, 

 whether obtained in the tropical climate of Jamaica or in the 

 temperate climate of England. Permeable seeds, according to 

 my observations, vary usually 3 or 4 per cent, of their weight. 

 Jodin found that in the course of a year's exposure to ordinary 

 air-conditions the water-contents of peas varied according to 

 the temperature and hygrometric condition of the atmosphere 

 from 10 to 30 per cent, of the seed's dry weight, or, as he puts 

 it, between o* i and 0-3 gramme for each gramme of water-free 

 material. Stated in terms of the wet weight, that is, of the 

 seed with its water-contents, this represents a variation of from 

 9 to 23 per cent., and an annual range of 13 or 14 per cent. 

 This hygroscopic range for peas during a year is considerably 

 larger than the range assigned to them in my own observations, 

 namely, 4 to 6 per cent. The difference is probably due as 

 much to the methods employed as it is to the differences in 

 the length of the experiments. Such a range was never 

 indicated in the case of the seeds of Canavalia ensiformis, the 

 total variation of which in a two years' experiment amounted 

 to less than 6 per cent, of their weight ; nor was it evidenced 

 in the course of my " long-period " weighing experiments, the 

 results of which are discussed in Chapter X. 



Serious obstacles are apt to arise in testing the maximum 

 capacity of a seed for absorbing water-vapour from the air. 

 They were encountered by Nobbe in his experiments on flax- 

 seeds (pp. 105-108). Such seeds, after being exposed for nine 

 days to air saturated with moisture, increased their weight by 

 1 6|- per cent., whilst others kept for the same period in ordinary 

 air added from ^ to i^ per cent, to their weight. In another 

 experiment on these seeds in saturated air, which covered 

 twenty-six days, it was found that under warm conditions 



