24 ELECTRICAL STRUCTURE AND 



such an advanced stage of development as the preceding 

 one, and the pod contained two seeds. 



Fig. 23. SECTION OF HORSE-CHESTNUT. [Original photo.] 



Two insulating membranes are shown, but there is a 

 third, not adherent to the seed, but lining the cavity in 

 which it lies, and designed, there can be little doubt, to 

 prevent a positive charge from reaching the immature 

 seed ; inasmuch as this membrane appears to be formed 

 before the membrane d attains the required resistance. 

 The function of the other two membranes, b and d, en- 

 closing the actively charged conducting layer, c, calls for 

 more elaborate if hypothetical explanation. 



Apart from the seed itself the major portion of the pod 

 is taken up by a white, pithy substance of positive sign ; 

 probably charged by the air through the epidermal spines 

 or pores. While the seed is growing it does not, I imagine, 

 require direct, but rather modified, electrical stimulus. 

 From the seed substance itself I obtained deflections of a 

 few millimetres only, whereas the conducting layer, c, gave 

 excursions of one thousand and over. Assuming, then, 

 that for some wise purpose possibly to give adequate 

 time for development stimulus to the seed substance is 

 modified, the function of the conducting layer, c, becomes 

 apparent, inasmuch as it would play much the same part 



