PLANT GROWTH. 7 



not appropriated by plants. When rain occurs after -severe 

 drought water may be taken up to some extent through 

 the leaf. 



Plants which have no chlorophyll cells, and possess 

 consequently no green colour, do not decompose carbonic 

 acid. We have familiar examples of such plants in the 

 broomrape and dodder of our clover fields, and in the 

 common fungi. The broomrape and dodder are fed by 

 the juices of the plant on which they live as parasites. 

 The fungi derive their carbon from the decayed vegetable 

 matter in the soil. 



Another important function of leaves consists in the 

 transpiration of water. This transpiration takes place 

 through small openings in the under side of the leaves, 

 known as stomata, which have the property of closing in 

 dry air and opening in moist. Transpiration takes place 

 only in light ; it will occur abundantly, even in an atmo- 

 sphere saturated with water, if the plant be only exposed 

 to sunshine. A small amount of general evaporation, dis- 

 tinct from transpiration proper, may occur in darkness. 

 The amount of water evaporated from the surface of a 

 growing plant is veiy large ; land that has borne a crop is 

 always much drier than a bare fallow. 



The results of transpiration to the plant are most im- 

 portant, the evaporation of water from the leaves being a 

 principal cause of the rise of the sap, and the consequent 

 drawing up of water from the soil containing plant food in 

 solution. 



Function of the Roots. — The roots of a plant are the 

 organs by which it absorbs water from the soil, and with 

 this water a variety of food elements are introduced. 



