38 GERMINATION 



Viewing the first sketch in plan the moist positive pith» 

 €, surrounds the negative tongue, /, and there is little or no 

 doubt that this is charged directly by the air through the 

 shell, which at all stages within the pod is conductive. 



The pod itself is composed of three layers, i.e., the outer 

 hard, but thin green coating, then a moist layer, l/8th to 

 3/16ths-inch thick, and a thin, white inner membrane lining 

 the cavity in which the nut lies. The second layer is positive 

 and connects only with the flower end of the pod. 



The inner membrane of the pod, instead of being chemi- 

 cally neutral, as in the case of the horse chestnut, is markedly 

 acid and it will be seen that when the nut is removed from 

 its pod the posterior half of the shell — calling the flower end 

 the apex — ^is always wet. I take it, therefore, that up to and 

 including this stage induction plays no part in the electri- 

 fication of the seed substance, but that the pod is directly 

 charged by the earth and the air, and that precautions are 

 taken, as before, to prevent more than a fraction of that 

 charge reaching the immature embryo. Corroboration of 

 this view is furnished by the third sketch which shows 

 the embryo shell in the form of a moist, green pigmented 

 layer, i, about 3/32nds-inch thick, between the membranous 

 covering of the seed substance and the iimer membrane of 

 the pod. 



,^J 



Walnut. — Transverse Section. 



After removal from the tree and therefore disconnection 

 with the earth, the pod in which the seed is contained con- 

 tinues to receive charge from the air but it has fulfilled 

 its purpose and thereafter induction is necessarily a factor 

 in the life history of the walnut. 



Both as a seed and a food, but more particularly in the 

 latter regard, it is interesting to observe the measures taken 



