PLANT SOCIETIES 





made, for some prefer sunn \ local imis, <>t hers shadv plaot 

 and so on. 



Plants which live in tin 

 called epiphytes (ep'l-fites : 

 plant) because they usu- 

 ally attach themselves 

 to the stem of a larger 

 plant. Their modifica- 

 tions consist of one kind 

 of roots for fixing them 

 to their support and 

 another capable of ab- 



air make up another group, 

 ( ircck. epii upon : phyton^ a 



sorbing and 



storing 



water. The latter or- 

 gans are called velamens 

 and are composed of 

 spongy tissue. They 

 are situated on the out- 

 side of the plant, soak 

 up rain and dew and 

 conduct it to an inner 

 region where it is used 

 as the plant needs it. 

 Velamens can also ab- 

 sorb moisture from the 



Figure 439. — Diagra- 



Sectional view of a branch infected 

 with mistletoe, showing the relation be- 

 tween the parasite and host ; a. branch 

 of host tree ; b. mistletoe ; c. primary 

 sinker; d, sinker from cortical root; 

 e, /, cortex of soft bark ; g, cambium 

 or growth ring; /;. wood of branch. 

 The starving and dwarfing of the branch 

 beyond the mistletoe is shown at ;'. 



air. The epiphytes are 

 characteristic of the tropics, where the air IS full of 

 moisture and where rains fall frequently. In OUT 

 own part of the world, lichens lia\ imewhal tin- 

 same habit, and orchids in greenhouses are another 

 example. 



The study of plants which deals with their distribution 

 and the factors which govern it is called plant < 

 (e-kol'o-jy : (J reck, oikos, home; hgo$, talk). 



