1918] on The Story of a Grass 301 



temperate zone, bat occurs in many tropical species and is charac- 

 teristic of Bamboos. If the branch-buds remain within the leaf- 

 sheath the new shoots are forced upwards, and a tufted or tussocky 

 habit results ; this is the cause of the tillering of cereals, and is 

 characteristic of steppe and savanna vegetation, and open places 

 generally in the warmer parts of the earth. In other cases the buds 

 soon break through the leaf-shcith, and then often grow horizontally 

 as long thin stolons: turf -formation is the result of such "extra- 

 vaginal" growth. Continued growth in length oi the stem is 

 locaKzed at the base of the internodes. The external sweUing, or 

 " node," belongs to the sheath, at any rate so long as the internode 

 above it is growing ; its function is the raising of culms which have 

 been " lain " by wind or otherwise. 



The rigidity of the hollow culm is due to a ring of strengthening 

 tissue just beneath the epidermis and round the conducting bundles. 

 The culm is an excellent adaptation for the rapid production of a 

 tough flexible stem of a temporary nature, with a minimum expendi- 

 ture of material. 



The character of the blade often reflects that of the environment, 

 thin and flat in shade-grasses, and narrow or often rolled where 

 exposed to strong sun or drying wind ; the structure of the blade 

 shows an interesting variety in this connection. 



The flower and the association of the flowers, or inflorescence, 

 supply a very characteristic feature of the family. The unit is the 

 spikelet, which contains one or more flowers. A comparison of the 

 grass-spike with an Iris bud or the spike of a Gladiolus indicates a 

 common plan of arrangement, and that the characteristic features of 

 the grass are the absence of coloured petals, and all that this absence 

 implies, and the development of the protecting bracts or " glumes " 

 Air-movements are the agents by which grass-pollen is transferred ; 

 the petals are reduced to small scales, the function of which is to 

 separate the protecting glumes to allow the stamens to emerge. The 

 beauty of the grass-flower is in many cases due to the colour of the 

 protruding, lightly hanging anthers. Some grasses are self-pollinated, 

 as generally wheat, and in some races of barley the flower never 

 opens. There is great variety in the form of the grass-inflorescence, 

 depending on the form of the individual spikelet (due partly to the 

 number of the flowers and partly to the form of the glumes), on the 

 presence or absence of stalks, and on the degree of branching. 



The fruit is also very characteristic : it rarely opens to discharge 

 the single seed, and is often united more or less with the glumes, 

 which aid in its distribution. In all wild grasses certain parts of the 

 spikelets or of the inflorescence fall off with the fruit. In the one- 

 flowered spikelet of Agrostis the axis separates above the empty 

 glume ; in the several-flowered spikelet of the Fescue the spikelet 

 itself breaks up. Where the spikelets are arranged in a close spike 

 the axis often divides so that one spikelet falls off with each joint, as 



