96 



SOCIAL CONJUNCTIVE SYMBIOSIS 



only in their symbiotic relation with a host and in their lack of 

 any connection with the soil. 



Epiphytes are especially characteristic of moist tropical regions. 

 In some tropical forests tree-trunks and large branches of trees may 

 be found that are as completely covered with vegetation as is the 

 surface of the soil itself, and the mass of roots and soil on such a tree- 

 trunk may be as much as a foot in thickness. While there are cer- 

 tain families of plants, such as the Orchidacese and Bromeliacese, 

 which furnish unusuallv large numbers of epiphytes there are 



Fig. 42. —Strangling roots of an epiphytic fig. (Photograph by William Trelease. 

 Courtesy of Dr. George T. Moore and the Missouri Botanical Garden.) 



representatives among the epiphytes of many other seed-plant 

 families as well as of ferns, mosses, liverworts, algse, and lichens 

 (Fig. 39.) In regions with winters or long dry seasons epiphytes are 

 relatively much less abundant and are limited almost entirely to the 

 lower forms of life, epiphytic ferns and seed plants being absent from 

 most regions outside of the moist tropics. 



Epiphytes very commonly possess certain structures that are char- 

 acteristic of plants of dry climates, such as well-developed organs of 



