THE STRUCTURE OF THE SEED 31 



e is an outer membrane or seed coat which afterwards turns 

 brown ; / an inner membrane or skin covering the seed 

 substance, and g the wall of the pod. The seed itself lies 

 in a bed of chemically neutral white pith. 



The stalk, the battery wire, makes contact with the seed 

 at the circular dot in the middle of Figure 14. 



While it is in its pod the seed substance must not be 

 electrified sufficiently to cause it to germinate. As yet it 

 is not ready to begin an independent existence. 



What are the precautions taken by Nature to prevent 

 this ? 



The earth supplies current as far as the seed coat ; the 

 layer c would take the place of the outer coating of tinfoil, 

 the inner membrane / the glass of the jar, and the seed 

 substance d, which also contains an acid secretion — the 

 inner coating of tinfoil. Why, then, is not the seed 

 adequately electrified. 



The reason is simple. In the first place, the layer c inter- 

 cepts the charge ; secondly, the patch of lighter colour on 

 the conker is of much lower resistance than the inner mem- 

 brane and therefore offers an easier path of escape than 

 the forced one of induction through the inner membrane. 

 We have a better view of the layer c, in the following sketch 

 of a younger seed and it will give us a clearer idea of the 

 stalk connection : — 



As a result the seed substance receives a very gentle 

 electrical stimulus, sufficient to enable it to grow, but quite 

 insufficient to urge it to premature germination. 



But when it has ripened, and the pod, falling, has split 

 segmentally and ejected the seed, a very important change 



