Root Action in Plants. 145 



D shows how the limp condition will permit the walls to 

 fall together. 



176. Loss of Water Through the Guard Cells. The epi- 

 dermis of the leaf is so close in texture and often so water- 

 proofed that when the guard cells close there is but little 

 loss of moisture. But when the sun shines and there is 

 moisture enough in the soil to keep the leaves from wilting 

 the guard cells open wide and great evaporation may take 

 place even in a saturated atmosphere. 



By admitting live steam into our plant house on bright 

 sunny days, keeping the air highly saturated, we have 

 found corn to lose nearly as much moisture as in the dryer 

 condition of the air with the sun also shining. The reason 

 this is possible is that the epidermis acts like the glass of 

 the hot bed, permitting the sunshine to enter but preventing 

 the longer dark heat waves from escaping. In this way 

 the air saturated outside is not so inside on account of the 

 higher temperature. This remarkable provision of the 

 plant to save moisture 'should teach how important it is to 

 assist, in every way practicable, the conservation of soil 

 moisture. 



STRUCTURE AND MODE OF ROOT ACTION. 



There is scarcely a better illustration anywhere in 

 Nature of the adaptation of living organisms to their en- 

 vironments than is furnished by the mechanism by which 

 the higher land plants supply themselves with moisture; 

 and one of the most remarkable of remarkable tasks is that 

 of a corn plant pumping into its stem and leaves, from a 

 comparatively dry soil, 2.896 pounds of water daily for 13 

 consecutive days. 



177. Functions of Roots. The roots of ordinary land 

 plants have three distinct functions to perform : First, to 

 gather from the soil its moisture and the salts dissolved in 

 it for the use of the plant; second, to convey and deliver 



