THE STEM. 



23 



Fig. 18 represents this tree, though comparatively few of 

 its stems are shown. We take the figure from Drummond's 

 Botany. 



Spiral, or Twining Stem, ( Caulis volubilis,) Fig - 19> 



Fig. 19. The Bean, the Hop, the Grape, 

 are familiar examples of this kind of stem. 

 Some plants turn to the right, and others to 

 the left, but in this respect they are governed 

 by invariable laws, that is, one plant of the 

 same species never twines to the right, and 

 another to the left. The Hop, for example, 

 turns round its pole, from the left to the right, 

 and if every plant of this species in a field be 

 examined, they will all be found to turn in the same direction. 

 To ascertain this, let the face be turned towards the south, 

 the east being on the left, and the west on the right. Then 

 it will be found that the hop vine makes all its volutions from 

 the left hand towards the right, that is, from the east towards 

 the west, or with the apparent motion of the sun. On the 

 contrary, the Bindweed, (Convolvulus] the Kidney Bean, 

 (Phascolus,} and many other vines, turn from the right to the 

 loft, or .against the motion of the sun. It is said that if these 

 plants are forced to grow in a contrary direction, that it 

 injures, and sometimes even kills them ! 



In hot climates, where vegetation attains its largest size, 

 there are some twining plants that strike the foreign traveller 

 with perfect astonishment. Mr. Bartram states, that in 



What are common examples of the spiral stem ? What invariable lav? 

 do twining stems observe with respect to turning to the right or left ? 



