504 



BOTANY 



are among the most striking. In these plants not only is the epider- 

 mis very thick, so as to check loss of water, but the leaves are often 



covered with scurfy scales, 

 which absorb water which 

 falls upon the plants, and 

 thus serve to supply part of 

 the loss due to transpiration. 

 The expanded leaf-bases, also, 

 serve as reservoirs of water. 

 In many epiphytic Orchids 

 there are developed thick 

 aerial roots provided with a 

 massive spongy root-cap which 

 serves the same purpose. 



Where plants grow very 

 much crowded together, as 

 they do in the moist forests 

 of the Tropics, the question 

 of light becomes a very im- 

 portant one, and many ways 

 have been developed in order 

 that plants may reach the 

 light. The epiphytic habit 



FIG. 472. Oncidium ornithorhynchum. An 

 epiphytic Orchid, showing the pseudo-bulbs 

 at the base of the leaves. (After BAILEY.) 



already described is a direct 

 response to the necessity for 

 light, and- in the forests of 

 the Tropics the branches of 



the trees are often completely hidden in the mass of epiphytic plants 

 which are trying to maintain their existence (PI. XI). These " air 

 plants" are of the most diverse kinds Mosses, Ferns, Orchids 

 (Fig. 472), Bromeliads, and myriads of other types. 



Climbing Plants 



Another method of reaching the light is shown by climbing plants, 

 which, like the epiphytes, reach their most perfect development in 

 the Tropics, although in our own forests there are many striking 

 examples. Climbing plants are either twiners, i.e. the stem winds 

 about the support, as in the Morning-glory or Hop, or there are 

 special climbing organs, tendrils, which may be branch-tendrils as 

 in the Grape or Virginia-creeper, or root-tendrils as in the Ivy and 

 Trumpet-creeper, or leaf-tendrils, e.g. Clematis, Vetch. The Legu- 

 minosae and Bignoniacese, represented in the United States by species 

 of Wistaria and Tecoma, in the moist forests of tropical America 

 include many " lianas " of gigantic size. 



