THE IMPERMEABILITY OF SEEDS 67 



cuticle is extremely unimportant and inconspicuous. In these 

 seeds the extreme resistance which they exhibit appears to be 

 located in the palisade cells.". . . The circumstance that the 

 seat of the chief resistance to the penetration of water may lie 

 in large seeds in the deeper tissues may explain how Dr Gola 

 comes to consider that this is the rule for impermeable seeds. 

 Miss White's investigations, however, establish the fact that 

 the seat of impermeability lies for most seeds in the structure- 

 less cuticle, a conclusion previously indicated, but on less 

 extended grounds, by the inquiries of Nobbe and by those of 

 Bergtheil and Day. 



SUMMARY 



(i) The frequency of impermeability in seeds of certain families, 

 especially of the Leguminosa;, which was first indicated by Nobbe a 

 generation ago, has within the last few years been established by Gola, 

 an Italian investigator. His results bring out the facts that, though 

 more typical of some genera than of others, impermeability is not a 

 generic character, and that it is rarely even a specific character, since 

 both permeable and impermeable seeds are commonly found in the 

 same species (p. 57). 



(2) Another of the inferences of Nobbe that delayed germination is 

 due in many cases to the impermeability of the seed-coverings to water 

 has been confirmed and extended by the recent researches of Crocker 

 in America. After this point, questions affecting seed-impermeability 

 usually resolve themselves into matters concerning seed-longevity. 

 Crocker rejects the idea that a seed's long life is as a rule to be 

 attributed to embryo characters or to the dormancy of protoplasm 

 (p. 60). 



(3) However, Ewart in Australia, after very extensive researches, 

 arrived at the conclusion that the longevity of seeds depends not on 

 their coverings, but on the persistence of the protoplasmic constitution 

 of the embryo or kernel ; and he views impermeability of the coats as 

 an adaptation for ensuring the long life of the seed under soil-conditions 

 (p. 61). 



(4) Of the 2500 species (more or less) with which Ewart deals, either 

 directly or through the observations of others, rather less than i per 

 cent, are long-lived seeds that will retain their germinative capacity 

 from fifteen to one hundred years and over. Of these " macrobiotic " 



