158 



STUDIES IN SEEDS AND FRUITS 



My observations on the hygroscopic behaviour of seeds are 

 naturally concerned only with permeable seeds, since the 

 impermeable seed in the usual sense of the word is non-hygro- 

 scopic, and when employed in experiments merely serves to 

 give contrast to the results. Hygroscopic seeds weighed daily 

 during a fortnight of changeable weather usually vary ij or 2 

 per cent, of their average weight, an amount, however, which 

 is only about half of what may be regarded as the ordinary 

 extreme of the hygroscopic range, which, as ascertained by 

 a method to be subsequently described, is usually 3 or 

 4 per cent. This reaction figures as a possible disturbing 

 cause in all experiments on seeds where the balance is 

 employed. 



Seeds as a rule continue to lose weight by drying during a 

 period varying from a few weeks to two or three months after 

 being gathered from the plant. If we extend the experiment 

 over a year or more, employing only seeds that have completed 

 the drying process and have acquired a stable weight, we find a 

 response to the varying humidity of the air not only in the 

 minor changes during short intervals, as between day and 

 night, and in the greater changes from week to week, but 

 also between the different seasons. It may here be remarked 

 that the seasonal changes in weight were well exemplified 

 in my experiments on the seed of Msculus Hippocastanum 

 (Horse-chestnut). Seeds that had been kept for three years 

 were usually i or i J per cent, heavier in the winter than in 

 the summer. 



Reference will now be made to the changes of weight 

 which many seeds undergo in transference between regions 

 where different hygrometric regimes prevail, as between 

 tropical and temperate countries. I made some observa- 

 tions in this direction in the case of seeds taken from 

 England to Jamaica in November 1907, seeds which had 

 been gathered fresh in Jamaica in the spring of the same 

 year. Permeable, impermeable, and variable seeds were here 

 represented. 



