Ch. IV, 10] 



FOLIAGE-BEARING STEMS 



185 



adherent disks, as with Virginia Creeper, or by disks on the 

 ends of aerial rootlets as in the Ivies which grow upon 

 buildings (Fig. 180). Others are twiners, and wind their 

 very slender stems around the support, as do Morning Glory 

 and Dutchman's-pipe. Some special forms of irritability are 

 concerned in the climbing movements. Thus, vines which 

 climb against walls have the stems negatively phototropic, 

 and thus are kept against the surface to which their 

 roots adhere. 

 All climbing 

 stems remain 

 slender, form- 

 ing new wood 

 but slowly, and 

 possess, as a 

 rule, verjr large 

 ducts. 



From the 

 climbing to an 

 epiph3rtic habit 

 there is every 

 gradation in 

 tropical vege- 

 tation. Epi- 

 phytes are 



plants which have no connectioii of their own with the ground, 

 but hve supported towards the light upon others, without 

 being parasitic. Very few occur in the flora of temperate 

 regions, aside from a few stray Mosses, Lichens, and other 

 low forms, but most tropical Orchids, some Ferns, and 

 many members of the Pineapple Family, including the 

 "Long Moss" of the South, are tj^Dical epiphytes ; and they 

 often cover the branches of tropical trees in great variety and 

 profusion (Fig. 126). Their mode of life is peculiar, and many 

 striking adaptations thereto have been described by those 

 who have studied them in the tropics. Their attachment to 



Fig. 127. — AUchmea viiniata var. discolor, typical of 

 the funnel-form epiphytes. (From Bailey.) 



