54 THE BOOK OF NATURE STUDY 



(iv.) CLIMBING. Some plants climb by twisting their leaf- 

 stalks round any object with which they come in contact. The 

 Garden Nasturtium (Tropceolum) and the Clematis are the best 

 known instances of this. It is this power of climbing that helps 

 the Clematis to reach the luxuriance it does in Gloucestershire 

 and Somersetshire, although something too depends on the soil. 

 Many of the Leguminosae develop tendrils in the place of leaflets 

 for the same purpose, e.g. the Peas, the Vetches. 



CLASSIFICATION OF LEAVES. So far foliage leaves have been 

 the most fully discussed. In botanical language, however, the 

 term " leaf " includes not only foliage-leaves but also seed-leaves 

 or cotyledons ; bud scales and the bracts which protect flowers ; 

 floral-leaves, namely, sepals, petals, stamens, and carpels. It was 

 Goethe who first saw the identity of origin amidst this diversity 

 of structure. In his treatise on The Metamorphosis of Plants, 

 written in 1790, he shows that all these structures stand in the 

 same relation to the stem, they are all developed laterally from it. 

 This generalisation gave the impetus to other similar researches, 

 hence hairs and prickles being developed from the epidermis are 

 now regarded as structures analogous to each other. Similarly, in 

 the animal world, the fur of the rabbit, the scales of fishes, the 

 feathers of birds, being alike in origin, are equivalent to each other 

 morphologically, although the function of each is very different. 

 Enough has already been said about cotyledons and bud scales, 

 but not about the bracts which form the involucre of flowers, or 

 of inflorescences. In the Composite, the minute florets are 

 protected by bracts which overlap each other and are often fringed 

 with hairs that conduct the water down from the bud. In this 

 order, some arrangement of the kind is necessary, for the sepals of 

 the flowers are very much reduced, and instead of protecting the 

 essential organs of the flower, they become an organ of dispersion. 

 These flower-heads of the Composite often close at night or in 

 wet weather, then the bracts are erect, completely enclosing the 

 florets ; when the flower-heads are open, the bracts are more 

 spread out, allowing the flowers to expand. Linnaeus observed that 

 the Dandelion opened from five to six in the morning and closed 

 some time between eight and ten, that the Goat's Beard or John- 



