12 



THE EOOT 



known as epiphytes or air-plants (Chapter XIII). The 

 most familiar examples are some of the tropical orchids, 

 which are grown in glasshouses. Fig. 13. 



33. Some plants throw 

 out aerial roots, which 

 propagate the plant or 

 act as braces. The 

 roots of Indian corn are 

 familiar. Fig. 14. Many 

 ficus trees, as the banyan 

 of India (Figs. 15, 16), 

 send out roots from their 

 branches ; when these 

 roots reach the ground 

 they take hold and be- 

 come great trunks, thus 

 spreading the top of the 

 parent tree over great 

 areas. The mangrove 

 tree (Fig. 17) of the 

 tropics grows along sea- 

 shores and sends down 

 roots from the overhanging branches into the shallow 

 water, and thereby gradually marches into the sea. The 

 tangled mass behind catches the drift, and soil is formed. 



REVIEW. What is the root for ? What is a root system? Define 

 tap-root. Fibrous root. What determines how deep the root may go? 

 How far does the root spread ? Explain what form the root sys- 

 tom may assume; also what extent. Where are the greatest num- 

 ber of fine roots found ? Where is the feeding surface of roots? Of 

 what use to the plant are the old woody roots? What are root- 

 hairs? What do they do and what becomes of them? What are aerial 

 roots? Where found? What are epiphytes, and where do their 

 roots grow? What are brace roots? How do the banyan and man- 

 grove spread (aside from seeds)? 



NOTE. The pupil should see the root-hairs. A week before this 



17. Mangroves marching into the sea. 



