86 STUDIES IN SEEDS AND FRUITS 



It would indeed appear that this is an ancient attribute of 

 seeds which they are now in process of discarding. 



A consideration that gives additional force to this line of 

 thought is that one of the greatest foes to the development 

 of impermeability in seeds is mould or mildew. These 

 minute fungi, when they establish themselves in the tender 

 skin of the soft, so-called unripe seed, either bring about the 

 death of the embryo before the resting stage is reached, or 

 give rise to a resting seed, with permeable coverings, which, 

 unless conditions favouring germination quickly follow, becomes 

 at length a shrunken, lifeless seed. (See Note 7 of the 

 Appendix and Chapter V.) From this standpoint imperme- 

 ability in seeds might be regarded as a decreasing quantity 

 in the plant -world, that is, if minute fungi have become 

 predominant only in the later ages of the earth's life-history. 

 One could conceive how, as a character of seeds, impermeability 

 might thus be banished from our planet, and the permeable seed 

 reign supreme ; and quite in harmony with this conception 

 would be the indication that Australia, the land of droughts and 

 the home of the Acacia, oiFers especially favourable conditions 

 for the persistence of impermeability in seeds and for securing 

 their longevity. However, the decision concerning these 

 views lies with the investigator of the future, and so we will 

 let the matter rest. 



SUMMARY 



(i) In order to introduce the subject of the contrast between 

 permeable and impermeable seeds, I have taken the very divergent 

 behaviour, as mainly revealed by the balance, of the seeds of tw^o 

 leguminous plants, that of Canavalia ensiformis as a type of the per- 

 meable seed, and that of Guilandina bonducella as a type of the 

 impermeable seed (p. 69). 



(2) Dealing first writh the seeds in their coats, the following 

 differences in their behaviour are described : — 



(«) The seed of Canavalia ensiformis swells readily in water and 

 possesses a stable weight subject to the normal hygrogcopic 

 variation (p. 70). 



