38 COMPOUND ORGANS OF PLANTS. 



persistent, and sometimes very thick, whilst with us they are 

 very slender and herbaceous and perish annually. Heat and 

 humidity are powerful agents in promoting vegetation, and 

 hence its superior activity in the tropics. 



The roots emitted "by the aerial portion of the axophyte 

 sometimes remain free and floating in the atmosphere, and . 

 sometimes they descend as far as the soil, which they penetrate 

 in order to draw from it additional nourishment. These pecu- 

 liarities are observable in many of the vegetables of the warm 

 and sunny South. A great many palms, figs, and orchideous 

 plants develope these roots. 



When the roots continue aerial, the plants are termed 

 epiphytes (Hfti upon, and tywtov plant). They are so called 

 because they grow to other plants as mere points of attach- 

 ment, dropping their roots into the atmosphere from which 

 they derive all their food, and which always continue aerial- 

 and greenish, and to distinguish them from parasites, which 

 obtain their nutriment from the plant on which they are found. 

 These plants abound in the tropical forests of South America, 

 which they enrich and beautify by their gorgeous and fragrant 

 flowers. That the trees on which they grow are mere points 

 of attachment, and not sources of food, is evident from the fact 

 that they may be attached to any substance whatever, as for 

 instance to the rafters of the stove or hot house, where they 

 will grow with an equal amount of vigor and luxuriance. 



The roots of the epiphytes or air-plants as naturally avoid the 

 ground and darkness as the roots of other plants seek for the 

 same ; they require air and light, and may be seen searching 

 for it in the warm, moist atmosphere of the conservatories, 

 through the crevices of the baskets filled with chips and char- 

 coal in which they are generally kept. In other instances, 



