GRAMINE^ (pOACEjE), GRASS FAMILY 73 



when its stems are bent over and caused to lie on the ground 

 by the mechanical action of a high wind, or driving rain. 

 Some grasses lodge more easily than others. This may be 

 due either to their greater height, heavier fruiting head, or 

 to a lack of strengthening material. Moreover, it has been 

 shown that an excessive amount of available nitrates in the 

 soil favors lodging. As it has been demonstrated that the 

 application of nitrate fertilizers to a soil tends to suppress 

 the amount of silicon taken in by the wheat plant, the greater 

 frequency of lodging of plants grown on such a soil may re- 

 sult from a stem weakness caused by a lack of silicon within 

 them. However, the causes of lodging are not well known. 



The stems of lodged grain are not necessarily broken. 

 The reverse is the case, as is shown by the fact that the lodged 

 culm has the power of partially or entirely erecting itself. 

 This power is exhibited more strongly in growing or imma- 

 ture culms than in old ones. When a grass stem is lodged, 

 the cells on the lower side of each internode, at its base, 

 grow more rapidly than those on the upper side, and, hence, 

 the stem curves upward. This behavior is a response to 

 the stimulus gravity. The manner in which gravity acts 

 upon an organ as a stimulus has not been demonstrated. 

 However, it has been experimentally determined that all 

 plants make pronounced adjustments in their growth in 

 response to gravitation. This property is called geotropism. 



Tillering. — It is a common observation that trees, shrubs 

 and most herbaceous plants produce side branches in regular 

 order, and that these arise at the nodes along the stem. The 

 side branches of the grasses are not so obvious as those in 

 trees and shrubs, for example, for the reason that the culms 

 of most grasses produce branches from the lower nodes only. 

 This branching in grasses is known as "stooling," "tillering," 

 or "mooting." The individual branches are known as "tillers" 



