COMPOSITION OF SOME INDIGENOUS GRASSES. 229 



growth as possible, an increasing state of general maturity was 

 almost inevitable even though the iiowers were still at the desired 

 stage. 



General, Ecological Notes. 



Many of the foregoing results may be explained and correlated 

 if, in addition to considering the general habitat and classification 

 of the various grasses, attention is also directed to the differences 

 in growth form and ecological life history. 



The ruderal grasses which occupj^ relatively high positions of 

 merit in Tables 11 and 111 in the main are annuals — for example, 

 Digitaria sanguinalis, Elcusine indica. Any annual plant has a 

 widely different physiological behaviour from a perennial. An 

 annual does -not store food in its underground parts. It grows 

 quickly and luxuriantly during the favourable — that is, summer — • 

 season. It provides for abundant seed production, but until the 

 seed begins to form it retains its stored-up food material in its 

 aerial parts, where it is available for the plant's use. Much 

 sclerenchyma, therefore, is not called for in the structure of such 

 annual grasses. Hence the value of such grasses is necessarily 

 high, both on account of the small amount of fibre present and 

 of the food material stored up, where it is so readily accessible 

 to grazing animals. From these same considerations one would 

 also expect to find considerable variation in these annual species, 

 and this is borne out by the figures in Table IV. Annuals, too, 

 are more readily affected in their composition by weather changes 

 than are perennials, due also to this storage of food materials in 

 their aerial parts. A perennial having its underground supply to 

 draw upon during unfavoui'able conditions and for seed foi'mation 

 naturally shows a greater stability in its composition. 



The general similai'ity of veld species may be correlated with 

 the general similarity of growth, being of a tufted or bunched 

 habit, while the ruderal species show greater variability in their 

 gi'owth forms. Their successional behaviour differs, however, 

 pioneers being more deep rooted and xerophytic, thus calling for 

 considerable sclerenchyma formation. Species that follow them 

 have a shallower rooting habit, and in their earlier stages demand 

 shade, their sclerenchyma requirements being therefore less. 



Another grass of high nutritive value is Cynodon dactylon, a 

 perennial creeping form which roots at the nodes. It requires 

 food storage for the perennial renewal of growth, but the food is 

 stored above ground, where it is within reach of grazing animals, 

 there being little underground growth. This creeping habit, then, 

 may be correlated with a less development of sclerenchyma for 

 strengthening purposes, and the rooting at each node means a 

 less distance for water conduction and less lignified conductive 

 tissue. 



Vlei grasses are generally of fairly high nutritive value, which 

 may be considered in relation to their habitat. Their water supply 

 is normally abundant, so that any great development of water 

 conducting tissue is not needed. Leersia hexandra, however, is 



