268 



ELEMENTARY STUDIES IN BOTANY 



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 

 character. Sometimes root systems developing in the soil 

 may enter tile drains, when water-roots will develop in such 

 clusters as to choke the drains. The same bunching of water- 

 roots may be noticed 

 when a hyacinth 

 bulb is grown in a 

 vessel of water. It 

 is evident that con- 

 tact with abundant 

 water modifies the 

 formation of roots, 

 both as to number 

 and character. 



(3) Clinging roots. 

 Such roots fasten 

 the plant body to 

 some support, and 

 may be regarded as 

 roots serving as ten- 

 drils. In the trum- 

 p e t-c reeper and 

 poison-ivy these ten- 

 dril-like roots cling 

 to various supports, 

 such as stone walls 

 and tree trunks, by sending minute branches into the 

 crevices. In such cases, however, the plant has also true 

 soil roots. 



(4) Air-roots. Some plants have no soil connection at 

 all. In- the rainy tropics, where it is possible to obtain 

 sufficient moisture from the air, there are many such 

 plants, notable among which are the orchids, to be observed 



FIG. 230. An orchid with aerial roots. 



