HYGROSCOPICITY 163 



action, excluding seeds like those of Ipomosa pes-capra^ where 

 the covering of hairs would give hygroscopicity, though the 

 seed bared of hairs is non - hygroscopic. The influence of 

 hairs is dealt with a few pages further on. 



Since impermeable seeds are not infrequent in nature, as 

 is shown in Chapter III, it follows that a large number of 

 seeds fail to make any response to the weather changes, and 

 are therefore non-hygroscopic. Here would belong the seeds 

 of many of the Australian Acacias and a number of the 180 

 " macrobiotic " or long-lived seeds included in Professor Ewart's 

 list {Proceedings, Royal Society of Victoria, 1908), though a large 

 proportion also would belong to the Variable Group, where 

 plants possess both permeable and impermeable seeds. 



As illustrating the behaviour of impermeable seeds in 

 the balance, there are appended the actual results obtained in 

 the case of those of four species during periods of from ten 

 to sixty days. It will be noticed, as before remarked, that 

 the same slight variation of from o*i to o"2 grain is displayed 

 by large and small samples, being evidently in great part 

 instrumental. We are here only concerned with the absence 

 of the ordinary hygroscopic reaction in the course of a few 

 weeks. The extent to which this behaviour is persistent will 

 be discussed in Chapter X. 



[Table 



