CHAPTER III 



THE IMPERMEABILITY OF SEEDS AND ITS SIGNIFICANCE . 



THE impermeability of seeds has occupied the attention of 

 many able investigators, but usually in connection with some 

 other character. They have not, however, always been in 

 agreement as to the meaning to be attached to the term 

 " impermeable," a fundamental difference which is reflected 

 in their occasionally inconsistent conclusions. In this work 

 a seed is regarded as impermeable only when it is able to 

 resist the penetration of water during an immersion of weeks 

 or months. 



Nature supplies abundant evidence of the impermeable 

 character of certain seeds in the floating drift of ponds and 

 rivers and of the ocean currents ; and many inquirers in their 

 observations and experiments on seed -buoyancy have dealt 

 indirectly with this subject ; but as it would be out of place 

 to allude to their results here, I would refer the reader for 

 a detailed treatment of the matter to my book on Plant 

 Dispersal. It should, however, be remarked that imperme- 

 ability may be equally a quality of the seed that sinks and 

 of the seed that floats, its connection with buoyancy being 

 only of an indirect character. 



I will at once proceed to deal with some of the aspects of 



the subject, on which recent investigations have thrown light. 



The fre- The frequency of impermeability in the case of seeds of certain 



permeability." families, especially among the Leguminosae, was established 



by Nobbe a generation ago in the pages of his work on 



56 



