THE GRASS FAMILY 



171 



were not done the plants would choke one another. This process 

 also forces the plant to form more numerous and stronger roots 

 which are Jielpful for a rich crop. 

 Adventitious roots grow freely out 

 of the lower nodes of the stem. 



The plants soon produce stems, 

 called culms, usually three to four| 

 feet long. Although they are very 

 thin, they are strong enough to bear 

 the weight of their leaves and that 

 of the grain in the panicles. They 

 are elastic and, when blown to and 

 fro by the wind, suffer no injury. As 

 in the stems of the Labiatie (p. 105), 

 it is the outer part of the stem that 

 suffers the greatest pressure when 

 bent. Those plants, therefore, have 

 the four edges of their stems strength- 

 ened by strong fibres. In the grass 

 culm a 7^02md tube is formed by such 

 strong fibres. The tissue in the 

 middle disappears, as it has to bear 

 no pressure wnen bent: the culm is 

 hollow. Only the nodes are solid and 

 divide the culm into various parts, 

 called internodes. This serves to 

 strengthen it. That part which is 

 to suffer the greatest tension, namely 

 the base of the culm, has its nodes 

 nearest together in order to make it 

 stronger at that particular part. — 

 Paddy has its roots under water; 

 and these must be supplied with air 



(see Lotus, p. 3), which is done by air- withitsleavesandinflorescence(F/.) 



chambers and canals running through ^'^''^ "^^^^^ *'^" protection of the 



the tissue of the stem and of the 



leaf-sheaths. 



Fig. 158. — Longitudinal section of 

 a voung Grrass-culm. The stem {St.) 



sheaths (S/f.) of the older leaves. 

 L. Ligule. (Natural size.) 



