446 PROCEEDINGS OF THE 



Toivtisendi, whose long spreading roots and stolons bind the soil 

 together, while the thick stems and leaves collect flotsam, and 

 so, in time, reclaim the land; sand dunes, on \vhich marram 

 grass grows, and by sending out its long roots and runners may 

 so consolidate the sand that other plants are able to grow there. 

 This grass, even if it becomes covered up by the drifting sand, 

 will grow right up through it. Agropyron juncewn, though not 

 so common, will stand the sea spray even better. The woody, 

 tree-like bamboos are common in Asiatic jungles, and there is 

 often a. bamboo zone on the m^ountains of tropical Africa and 

 the Andes. 



The leaves of grasses are arranged in two alternate rows. 

 Shoots are produced, as usually, in the axils of the leaves. Barren 

 shoots never occur on annual grasses. The shoots may grow up 

 within the leaf-sheath (intravaginal) or they may break through 

 and spread laterally from the base (extravaginal). The first 

 method of growth gives rise to isolated tussocks characteristic 

 of a warm climate (steppes and savannahs), the second method 

 produces turf and sods such as we find in a cool or temperate 

 climate. 



The grass stem, or " culm," grows not only at the tip, but at 

 the bases of the internodes, where the soft, growing tissues are 

 supported by the leaf-sheaths. The " nodes " are thickenings of 

 the leaf-sheaths, and their function is to raise the culm to an 

 erect position if it should become bent. They consist of thin- 

 walled, strongly turgescent tissue, which is sensitive to the force 

 of gravity. When the culm is horizontal or oblique the cells of 

 the node on the side turned towards the earth begin to lengthen ; 

 the lower side thus becomes longer, while the upper side is short- 

 ened from pressure on the opposite side. Several nodes may 

 share in this process, which goes on until the upper internodes 

 have resumed the vertical. The typical grass stem is hollow, 

 and rigidity is given to it by bands of thick-walled tissue. This 

 structure is adapted for the production of a tough, flexible stem 

 with a minimum expenditure of material. This stem has to last 

 long enough to raise the leaves and i florescence into the air 

 and be flexible enough to allow swayi.ig in the wind witliout 

 breaking, which changes the air round the leaves, and thus assists 

 in the process of feeding, and also in the distribution of the pollen, 

 and later of the fruits. This economical manner of growth is 



