BOOTS 



99 



cient moisture from this source, without any soil-relation 

 or water-relation. Among these plants the orchids are 

 most notable, and they may he observed in almost any 

 greenhouse. Clinging to the trunks of trees, usually imi- 

 tated in the greenhouse by nests of sticks, they send out 

 long roots which dangle in the moist air (see Figs. 93, 94). 

 It is necessary to have some special absorbing arrange- 

 ment, and in the orchids this 

 is usually provided by the de- 

 velopment of a sponge-like 

 tissue about the root known 

 as the velamen, which greed- 

 ily absorbs the dew or water 

 trickling down the plant. See 

 also Figs. 92, 95, 96, 97. 



67. Clinging roots. — These 

 roots are developed to fasten 

 the plant body to some sup- 

 port, and do no work of ab- 

 sorption (see Fig. 98). Very 

 common illustrations may be 

 obtained from the ivies, the 

 trumpet creeper, etc. These 

 roots cling to various supports, 

 stone walls, tree trunks, etc., 

 by sending minute tendril- 

 like branches into the crevices. The sea-weeds (algae) 

 develop grasping structures extensively, a large majority 

 of them being anchored to rocks or to some rigid support 

 beneath the water, and their bodies floating free. The 

 root-like processes by which this anchorage is secured are 

 very prominent in many of the common marine sea-weeds 

 (see Fig. 162). 



68. Prop roots. — Some roots are developed to prop 

 stems or wide-spreading branches. In swampy ground, or 

 in tropical forests, it is very common to find the base of 



Fig. 94. An orchid, showing 

 roots and thick leaves. 



