6 FERTILIZERS 



RESPIRATION. 



2. Plants have a respiratory system. They ab- 

 sorb oxygen and give off carbonic acid, mostly at 

 night, but during the day more oxygen is given off 

 and carbonic acid absorbed. The leaves and some of 

 the green bark are the respiratory system. Carbon 

 and oxygen thus enter the plant directly from the air 

 as well as by water from the roots. 



FIGURE 1 

 TRANSPIRATION. 



3. Plants give off water (Transpiration) at all 

 times of day and night. The water escapes at cer- 

 tain pores, called Stomata, of the leaf contained also 

 in very young bark. Water carries the plant food 

 into the plant by way of the roots. The plant foods, 

 changed and elaborated, are retained in the tissue as 

 new growth while the water passes off through 

 the leaves as a vapor. When transpiration exceeds 

 the supply from the roots the plant wilts. If the air 

 is saturated with moisture, plants give off less, but 



