PROCESS OF NUTRITION. CHAP. HI. 



increased in size very considerably ; but the under 

 part which remained motionless increased very 

 little. A plant which was compelled to move in a 

 circle was found to have the greatest diameter of its 

 trunk in the direction of its motion. Hence Mr. 

 Knight inferred that the motion communicated to 

 plants by the action of the winds facilitates the 

 descent of the proper juice and consequently growth 

 of the plant; and that plants deprived of that 

 motion do not thrive so well, as in the case of 

 trees nailed to walls. It seems probable, however, 

 that the small degree of augmentation in the under 

 part of the stem of the seedling Apple-trees was 

 as much owing to its exclusion from air and light, 

 as to its want of motion ; as in the case of what is 

 termed the etiolation of plants, exemplified in the 

 slender stem of potatoes that may happen to pro- 

 trude their shoots in cellars or other dark places. 

 And trees nailed to walls are often as healthy as 

 standards, particularly Vines. 



To the waving motion of the plant Mr. Knight 

 also attributes the facility with which plants adapt 

 themselves to the habitats in which they grow. In 

 lofty and exposed habitats they will increase most 

 near the root, owing to the accelerated descent of 

 the proper juice ; they will send out many lateral 

 branches and diminish gradually towards the top ; 

 they will be low and sturdy. In groves and vallies, 

 where they are crowded and less exposed they will 

 extend in length without extending proportionally 



