DIFFERENT FORMS OF STEMS. 109 



spoken of as the root of the plant, being partly buried be- 



Fio. 56. CREEPING STEM OF FERN. 



neath the ground. The runners of the Strawberry, again, are 

 but trailing stems ; which 

 send down roots, and de- 

 velop buds, at intervals, 

 and thus extend the plant. 

 This tendency, which is 

 serviceable to Man in this 

 instance, is very trouble- 

 some to him in another ; 

 for in the same manner, 



FIG. 57. 



AN AQUATIC PLANT EXTENDING ITS STEMS 

 IN THE MUD. 



the Couch-grass overruns 

 pasture lands, exterminating, if its increase be not checked, their 

 original vegetation. As every internode of these trailing stems 

 possesses the power of developing both roots and buds, it is use- 

 less to attempt to destroy the plant by chopping the stem into 

 pieces ; for this is in reality only multiplying it. It is well to 

 mention, however, that though usually regarded as a very rank 

 weed, the underground shoots of this plant constitute a pecu- 

 liarly nutritious food for cattle. 



151. One of the most distorted forms of the Stem, is that 

 which presents itself in the Potato. This plant grows with an 

 underground stem, sending up its flowering branches into the air, 

 and sending its roots downwards into the earth ; but on this stem 

 it forms at intervals the tubers or knobs, which constitute such 



