94 THE MECHANICAL FUNCTIONS. 



absorption and of mechanical support. Both 

 these purposes are promoted by their sending 

 out from their sides numerous fibrils, or lesser 

 roots, which increase their firm hold upon the 

 soil, as well as multiply the channels for the 

 introduction of nourishment. 



Nature has supplied various plants with cer- 

 tain appendages to the above mentioned struc- 

 tures, the use of which are for the most part 

 sufficiently obvious. Of this description are the 

 tendrils, which assist in fixing and procuring 

 support to the stems of the weaker plants ; the 

 stipules, which protect the nascent leaves ; and 

 the bractece, which perform a similar office to the 

 blossom. The different kinds of hairs, of down,* 

 of thorns, and prickles, which are found on the 

 surface of different plants, have various uses ; 

 some of which are easily understood, particu- 

 larly that of defending the plant from molesta- 

 tion by animals. The sting of the nettle is of 

 this class ; and its structure bears a striking 

 analogy, as we shall afterwards have occasion to 

 notice, to that of the poisonous fangs of serpents. 



The purposes answered by the down, which 

 covers a great number of plants, are not very 

 obvious. It perhaps serves as a protection from 

 the injurious effects of cold winds on the tender 

 surface : or it may have a relation to the depo- 



* The finer hairs, and filaments of down, are composed of 

 elongated cells., either single, or^several conjoined end to end. 



