430 PROTECTION OF GREEN LEAVES AGAINST ATTACKS OF ANIMALS. 



TriticuTYi caninum. When the wind sways the leaves of these plants, the arch 

 formed by them is either narrowed or widened, according as the wind comes from 

 this or that side. In still air the leaf assumes a middle position. Although the 

 arch may be widened or narrowed by the wind, in no case does the bending go 

 so far as to break the blade. Moreover, these leaves are rendered so elastic by a 

 suitable arrangement of bundles of bast, that even violent storms cannot do them 

 much harm. These arched, overhanging, ribbon-like leaves are often further 

 complicated by the fact that all the leaves are turned to the same side so that they 

 present a combed appearance — like those of the reed — although their sheaths cannot 

 twist round the haulm. This is seen especially when the plants are growing on the 

 margin of a wood or on the narrow terraces of a rock face, i.e. on places where they 

 are only illumined on one side. The one-sided direction of the leaves is connected 

 with the illumination, and is due to the fact that a semi-arched leaf turned towards 

 the gloom of a wood, or towards a shady rock-wall, would not obtain suflBcient 

 light. This gives rise, indeed, to an inversion of the leaf-blade, so that the originally 

 lower side of the leaf becomes the upper. 



It is scarcely necessary to state that the relations with regard to light exercise 

 a no less important influence in the determination of the shape of the spiral and 

 fistular leaves than in the above-mentioned grasses, whose leaves are arched, over- 

 hanging, and partially twisted. If these relations are not taken into consideration, 

 it is not because the significance of light in these special instances is not appre- 

 ciated, but only because a clear view of these extremely complicated conditions can 

 only be obtained by a rather one-sided treatment 



PROTECTIVE AREANGEMENTS OF GREEN LEAVES AGAINST THE 

 ATTACKS OF ANIMALS. 



The matrix of the chlorophyll-granules is very similar in composition to that of 

 protoplasm, and, like it, consists of nitrogenous compounds; by the activity of the 

 chlorophyll-bearing cells sugar and starch are produced, and the green cells contain 

 not only albuminous compounds, but also carbohydrates, and these, too, in a form in 

 which they are digested with comparative ease. What wonder, then, that these 

 green cells furnish a very desirable food for innumerable animals. Many animals, 

 it is well-known, live exclusively on a vegetable diet, and principally on chlorophyll- 

 bearing tissues. On the other hand, the plants in question would perish with the 

 loss of all their green organs, especially if the store of reserve food in them were 

 also exhausted. The animal and vegetable kingdoms in this sense are at war with 

 one another. The instinct of self-preservation forces animals living on green 

 vegetables to seek their food at any cost, to seize the plants unsparingly, and 

 when their hunger presses, to destroy them root and branch. Herbivorous animals 

 cannot, like men, foresee that in the consumption of the means of subsistence the 

 plants robbed of all their green organs must perish, that consequently in the 

 following years for them and their descendants food will be wanting, and that 



