140 STUDIES IN SEEDS AND FRUITS 



examination proved that their kernels were in appearance 

 sound. A more careful test of their germinative capacity 

 might have produced different results. However, the interest 

 of the experiment lies in its suggestiveness as to the mode in 

 which an impermeable seed might be able to resist a temperature 

 of 1 00 C. Provided that its water-contents are reduced to 

 a minimum, it could withstand even a greater amount of heat 

 and yet germinate. Becquerel, basing his opinion on the 

 experiments of Dixon, considered 120 C. as the limit for 

 desiccated seeds (Annales des Sciences Naturelles^ v., 1907). 

 With regard to my own results it may be added that the loss 

 of weight in the oven is not so surprising as the subsequent 

 resumption of impermeability. Behaviour somewhat similar, 

 though under different conditions, is noticed below in the 

 case of the impermeable seeds of another plant. 



Another illustration of the method by which impervious 

 And by coats may enable seeds to resist high temperature was afforded 

 obtusifolia. by selected impermeable seeds of Canavalia obtusifolia under 

 the strain of a great variety of thermal conditions, both with 

 coats intact and with coats punctured, as shown in the diagram 

 below. Exposed to alternating dry and damp conditions at 

 ordinary temperatures and to extremes of dry and moist heat 

 in the oven, the seed with coats intact varied only about 1*2 

 per cent, of its weight during a period of seven weeks, whilst 

 the range of the weight of the seed with punctured coats 

 under the same tests and during the same period was 7-5 per 

 cent. But if we disregard the first loss of weight as concerned 

 with influences preceding the experiment, then the variation 

 under these highly contrasted conditions of the seed with 

 coats intact amounted only to 0*7 per cent., which is probably 

 not much greater than the variation that a quartz-pebble 

 would exhibit under the same circumstances. Since the 

 impermeable seeds of Canavalia obtusifolia normally increase 

 their weight by 5 or 6 per cent, when exposed to the air bared 

 of their coats, some proportion of the great variation displayed 

 by the punctured seeds must be ascribed to their original 



