PERMEABLE AND IMPERMEABLE SEEDS 



73 



by the bared kernels of nearly all impermeable seeds that have 

 been subjected to this test. The dry friable kernels when 

 coarsely broken up contrast greatly in their appearance with 

 the relatively moist and compact materials of permeable 

 seeds ; and hence it could be presumed without further 

 inquiry that absorption of water-vapour from the air is the 

 cause of the subsequent increase in weight. But this capacity 

 in seeds of becoming considerably heavier when exposed to 

 the air than when locked up in their impermeable coats 

 pre-supposes a condition of ultra-dryness within the seed 

 itself. We should thus expect that the seeds of Guilandina 

 bonducella, as types of impermeable seeds, would contain 

 much less water than typical permeable seeds, such as those 

 of Canavalia ensiformis. 



We have accordingly to appeal to the evidence of the oven An appeal to 

 in order to interpret the indications of the balance ; and in the of the oven, 

 table now to be given are to be found the results of exposing 

 these two kinds of seeds to a temperature of ioo° to 105° C. 

 for a period of from one and a half to two hours. 



Water-contents of a Typical Permeable and a Typical Im- 

 permeable Leguminous Seed as ascertained by Exposure to 

 A Temperature of 100° to 105° C. for i| to 2 hours. 



Note. — These results represent the combined water-contents of kernel and coats, 

 have omitted decimal fractional parts, as these values are dealt with in later chapters. 



These results establish the ultra-dryness of the seed of 

 Guilandina bonducella enclosed in its impermeable coverings ; 

 and we recognise in the absorption of water-vapour from the 

 air by the bared seed an attempt to assume the condition of a 

 permeable seed. As far as their water-contents are concerned, 



