68 GROWTH AND SECRETIONS. 



sorb a large quantity of water, or if the current 

 of the descending sap be materially lessened, as 

 will occur if it is in total darkness, then shoots 

 are obtained extraordinarily long and herbace- 

 ous ; as in the weeping willow, and in the 

 blanched plants of flax, cultivated for the finest 

 Flanders thread. On the contrary, if the quan- 

 tity of water be diminished, and the plant ex- 

 posed to the influence of such circumstances as 

 will increase the fixation of carbon, we obtain 

 shoots which are short, firm, and woody ; as 

 are seen in the dry and light situations of south- 

 ern climates and high mountains. It appears 

 from the above facts that the lengthening of the 

 shoots depends on the influence of the ascend- 

 ing sap, while from the richness of the descend- 

 ing current, and consequent deposition of nu- 

 tritive matter, arises its solidification and the 

 diminution or cessation of vertical growth. 

 Those plants which have the greatest tendency 

 to form wood, attain proportionately the soonest 

 to that state of hardness which arrests the 

 lengthening of the shoot; thus it is seen that 

 there is a sensible relation between the slowness 

 of increase in height in each tree, and the quan- 

 tity of carbon which it furnishes to combustion. 

 In herbaceous perennials, the nourishment, 



