THE ROOTS 45 



curious crinkled appearance, especially in the case 

 of orchids. This is due to the peculiar structure 

 of the outer layers of cells. In fact, these roots 

 have a layer of tissue not found in ordinary roots. 

 This outer tissue is composed of cells, which die as 

 soon as they attain full size, and the walls are 

 left, forming a layer of loose spongy tissue entirely 

 sheathing the root. The sj^ongy layer not only 

 absorbs drops of water which may fall upon it, 

 but will also gather water from the air when it is 

 humid and damp. The species furnished with such 

 roots usually live in localities which have much 

 rain, and their entire supply of water may be 

 gathered in these ways. 



50. Parasitic roots. — Many species have the 

 habit of fastening to the bodies of other plants 

 and drawing a part or all of their water and food 

 from them. They do not need the ordinary soil 

 roots, but have developed special forms which are 

 capable of piercing the bodies of their hosts, as the 

 plants on which they live are called. The mistletoe 

 is an example of this type ; but perhaps the para- 

 site most widely distributed in America is the 

 dodder {Cuscuta), which may be seen in damp 



