34 



COUN CROPS 



give off constantly large quantities of excessive water 

 taken up by the roots ; (3) to elaborate plant-food from 

 the minerals and water taken out of the soil, combined 

 with carbon and oxygen taken from the air ; (4) to ab- 

 sorb energy from the sun which is necessary in order that 



Mrrfrtb 



Mesophyll 

 tissue ~ 



Fig. 14. — Leaf structure. The movement of water and solutions takes 

 place through the fibro-vascular bundles. The mesophyll tissue fur- 

 nishes the means for elaborating plant-food from raw material. Inter- 

 change of air and gases takes place through the stomata. The bulli- 

 f orm cells are similar to mesophyll cells, but contain a large percentage 

 of water. Shrinkage of these cells causes the leaf to roll in dry weather. 



these activities may proceed. Each of the above functions 

 of the leaf requires specialized tissues which are briefly de- 

 scribed as follows (21, 22) : — 



21. The vascular system. — ^ If a maize leaf is examined, 

 there will be found running lengthwise a large*number of 



