OF PLANTS. 17 



nitely greater number of fibres and spongelets 

 are produced, than when the same plant is 

 grown in a moist and fertile soil. 



The fibres, like the leaves of trees, are pro- 

 duced annually, in some cases falling off like 

 leaves, as in the Dahlia; in others increasing 

 in size, and becoming harder like the parent 

 body of the root, and subsequently throwing 

 out new fibres themselves, as is the case with 

 almost all large trees. 



Besides this property of absorbing nutriment 

 from the soil, these fibres have the power of 

 throwing off that matter absorbed by the 

 spongelets which is either unnecessary or nox- 

 ious to the plant, and this may be one of the 

 causes Vvhich prevents plants of any kind from 

 being successfully cultivated on the same soil 

 during a succession of years. 



It may here appropriately be mentioned that 

 darkness, or at all events the absence of light, 

 is essential to the development of the fibres of 

 the roots. 



The stem is the next part to be considered, 

 but the functions it perforins in the vegetable 

 creation are so subordinate to those performed 

 by the root and leaves, that it will occupy but 

 little time to become acquainted with its of- 

 fices. 



The stem of all plants rises immediately 

 from the crown of the root, and is consequently 

 always above the ground. The same variety 

 prevails in this part of the plant as in the root, 

 for instance : the stems of wheat, barley, and 

 the grasses rise to some height and are termed 

 3 



