PERMEABILITY AND CLASSIFICATION 105 



Whilst showing in the preceding pages that to deficient 

 shrinkage must be attributed the origin of permeable seeds in 

 those plants where impermeability is more or less the rule, but 

 little allusion was made to the changes in the appearance and Changes in 



i . . r i T i the condition 



condition or the outer seed-coverings in this connection. O f the seed- 



Thus, in the case of deficiently shrunken seeds of Entada 

 scandens, the cuticle is traversed by a network of fine cracks ; lossofi " 1 - 

 and one of the earliest signs of a normal impermeable seed illustrated by 

 losing its impermeability is displayed in the development of 

 these fine cracks. But it is in the seeds of Guilandina bonducella 

 that we have the best opportunity, though under rather 

 peculiar conditions, of investigating this subject, and of 

 observing how deficient shrinkage deprives the seed-coats of 

 their impervious character. 



Whilst describing the stages in the shrinking process of 

 this seed in a previous chapter (Chapter II), when the con- 

 nection between deficient shrinkage and loss of impermeability 

 was first pointed out, no reference was made to the singular 

 changes in the condition of the outer coats then displayed. It 

 is very remarkable that the moist, swollen pre-resting seed of 

 the green unopened pod, though destined ultimately to become 

 impervious to water, develops during the earliest stage of the 

 shrinking process a number of parallel transverse fissures or 

 cracks in the outer coat, and that the seed is only impermeable 

 when these fissures become closed and hermetically sealed in 

 the contracted resting seed. In the normal resting seed the 

 cracks formed in the outer coats during the shrinking stage are 

 indicated by faint striae, now covered by the enamel-like cuticle ; 

 but in the deficiently shrunken seed the original cracks are 

 much more evident and are not sealed over by the cuticle, but 

 are more or less open, so that the seed is permeable both to air 

 and water. 



If we place in the sun one of these large, soft pre-resting 

 seeds from the green unopened pod, in a few hours its surface 

 will be traversed by regular and widely gaping transverse cracks, 

 and will present the grooved appearance of a boy's top. It is 



