178 STUDIES IN SEEDS AND FRUITS 



ever is one where a perfectly dry embryo is locked up in a hard 

 impermeable shell or covering (p. 157). 



(11) Coming to the details of his ow^n observations on hygro- 

 scopicity, the author, after observing that in the nature of things 

 considerations of hygroscopicity are concerned only with permeable 

 seeds, proceeds to discuss the effects of change of climate on the weight 

 of seeds. In this connection he shows that, as a result of transporta- 

 tion from the temperate zone to the tropics and back, permeable 

 seeds varied from 3 to 4 per cent, of their weight, variable seeds 

 (both types in the same plant) less than i per cent., and impermeable 

 seeds practically not at all. The changes of weight, he points out, 

 are included within the ordinary hygroscopic range (p. 158). 



(12) The methods of determining the range of hygroscopicity 

 in seeds in terms of the variation of their weight are then described, 

 and after giving the results of his observations on more than sixty 

 kinds of seeds, of all sizes and characters, he forms the following 

 general conclusions : — 



(«) That permeable seeds vary usually to the extent of from 2 

 to 3 per cent, of their weight, though the range may 

 be as little as i per cent, in equable atmospheric conditions, 

 and as great as 4 or 5 per cent, when the changes in the 

 relative humidity of the air are extreme ; 



[b) That impermeable seeds have practically no hygroscopic 



reaction, their weight remaining unchanged in spite of 

 great variations m the hygrometric state of the air ; 



[c) That with variable seeds, where there is a mixture of permeable 



and impermeable seeds, the range for any ordinary sample 

 is usually about i per cent., differing according to the 

 proportion of permeable seeds (p. 165). 



(13) Special stress is laid on the value of the hygroscopic reaction 

 stated in terms of weight as a test for proving seeds (p. 166). 



(14) Additional data are given, as supplementing those already 

 given in Chapter IV, on the influence of the coats on the hygro- 

 scopicity of permeable seeds, and supporting the previous conclusion 

 that the coats tend to restrain the hygroscopic range (p. 167). 



(15) Results of observations are then given on the effects of age 

 on the hygroscopic behaviour of seeds, and they are shown to be 

 slight (p. 168). 



(16) Contrary to one's expectation, it is found that a hairy covering, 

 whilst it gives a small hygroscopic range of less than i per cent, 

 to impermeable seeds, but slightly if at all increases the hygroscopicity 

 of permeable seeds (p. 169). 



(17) Since it follows from the principle of Berthelot that the water 

 of hygroscopicity could have little to do with germination, appeal 



