98 PLANT RELATIONS. 



Plants which ordinarily develop soil roots, if brought 

 into proper water relations, may develop water roots. For 

 instance, willows or other stream bank plants may be so 

 close to the water that some of the root system enters it. 

 In such cases the numerous clustered roots show their water 



Fig. 93. An orchid, showing aerial roots. 



character. Sometimes root systems developing in the soil 

 may enter tile drains, when water roots will develop m such 

 clusters as to choke the drain. The same bunching of water 

 roots may be noticed when a hyacinth bulb is grown In a 



vessel of water. 



66. Air roots.— In certain parts of the tropics the air is 

 so moist that it is possible for some plants to obtain sum- 



