IX. OUTSIDE AND IN. 1 8/ 



can report on it ; secondly, that all the increment 

 of tree stem is, by division and multiplication of 

 the cells of the wood, a process not in the least 

 to be described as 'sending down roots from the 

 leaf to the ground.' I suspected as much in be- 

 ginning to revise this chapter ; but hold to my 

 judgment in not cancelling it. For this multipli- 

 cation of the cells is at least compelled by an 

 influence which passes from the leaf to the ground, 

 and vice versa ; and which is at present best con- 

 ceivable to me by imagining the continual and 

 invisible descent of lightning from electric cloud 

 by a conducting rod, endowed with the power of 

 softly splitting the rod into two rods, each as thick 

 as the original one. Studying microscopically, we 

 should then see the molecules of copper, as we 

 see the cells of the wood, dividing and increasing, 

 each one of them into two. But the visible result, 

 and mechanical conditions of growth, would still 

 be the same as if the leaf actually sent down a 

 new root fibre ; and, more than this, the currents 

 of accumulating substance, marked by the grain 

 of the wood, are, I think, quite plainly and abso- 

 lutely those of streams flowing only from the leaves 

 downwards ; never from the root up, nor of mere 

 lateral increase. I must look over all my drawings 

 again, and at tree stems again, with more separate 



