CHAPTER V 



THE GROUPING OF SEEDS ACCORDING TO THEIR 

 PERMEABILITY OR IMPERMEABILITY 



HAVING introduced the subject of impermeability in the two 

 preceding chapters, 1 now proceed to discuss the grouping of 

 seeds according to the presence or absence of this quality. 

 We have already seen that impermeable and permeable seeds 

 are often found in the same plant. This is sufficiently frequent 

 to be regarded as quite a normal occurrence, the distinction 

 between the two types being occasionally accentuated by a 

 conspicuous difference in the external characters, thus enabling 

 two kinds of seeds to be recognised in a plant. Imper- 

 meability presents itself in a transition stage in so many plants 

 that one feels bound to regard it as an attribute that is either 

 being gradually discarded or being gradually developed ; and 

 indeed the question whether seeds are now in the act of 

 acquiring or of dispensing with this quality was the dividing 

 issue raised at the close of the previous chapter. 



It will thus be seen that we cannot divide all seeds between 

 two groups, permeable and impermeable, since there is a large 

 intermediate group where the two kinds of seeds are associated. 

 It is this variable group that will offer some of the best oppor- 

 tunities of observing the stages in the development or in the 

 degradation of impermeability, as the case may be. But seeds 

 belonging to the impermeable group will also be of assistance 

 in this inquiry, since, although normally impermeable, they 

 present at times in their defectively shrunken seeds good 

 materials for study. 



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