MOVEMENTS AND ATTITUDES OF PLANTS 147 



a plant fixes itself to a support. They may be modifica- 

 tions of (1) branches, e. g. Passion Flower, Vine, Virginia 

 Creeper, and White Bryony ; (2) leaves, e. g. the Chick-Pea ; 

 (3) petioles, e.g. Clematis; (4) leaflets, e. g. Sweet-Pea, Vetch, 

 and Garden Pea ; or (5) stipules, e. g. some species of Smilax. 



Sun and shade positions. If you note the differences of 

 position of leaves in sunny places and compare these leaves 

 with others of the same kind growing in the shade, you will 

 see that they take up a favourable position with reference 

 to light. Fig. 95 shows two shoots of Gooseberry taken 

 from different sides of the same plant. One (1) was over- 

 shadowed by branches of an apple-tree, and exposed its 

 leaves fully to the available light. The other (2) was not 

 overshadowed, and its leaves moved in such a way as to 

 expose the edges of their blades to the direction of the sun's 

 rays. As chlorophyll is decomposed by strong sunlight, 

 it is an advantage to a plant organ to assume a position 

 whereby the smallest surface is exposed to the direct rays 

 of the sun. 



Fixed light position. Some Acacias (Fig. 96, 1) growing 

 in sunny regions have curiously modified leaves, which 

 persistently turn their edges to the sky and give a char- 

 acteristic appearance to the plants. The blades are not 

 developed, but the leaf-stalks are flattened out and become 

 leaf-like, and are called phyllodes. The attitude assumed 

 by the foliage of a plant with reference to light is called 

 the ' fixed light position '. In some plants the leaves are 

 reduced to scales, the stems flatten out, resemble leaves, 

 and, as in the Acacias, turn their thin edges to the sky. 

 Such leaf-like stems are known as phylloclades, and occur 

 in the Butcher's Broom. Other examples are the Smilax 

 (Myrsiphyllum) (Fig. 96, 2) and species of Asparagus. 

 Extraordinary examples occur in Cacti (Fig. 96, 3) and 

 other desert-plants. The huge fleshy stems are green, 

 store a large supply of water, and do the work of foliage- 



K 2 



