h,} BOTANY OF THE LIVING PLANT 



necessary to observe some order and method in the study of parts so 

 variable. The classification of parts of the Plant will be taken up 

 in Chapter XX. : meanwhile a few examples illustrating the adapt- 

 ability of the plant will be described in the present chapter. But it 

 would be impossible in such a book as this to treat so wide a subject 

 exhaustively. It must suffice to refer to the Natural History of Plants, 

 by Kerner and Oliver (Blackie & Son, 1895, 4 vols.), where many 

 adaptive features of plants are described and illustrated ; or for the 

 consequences of adaptation as shown in the distribution of British 

 Plants to Types of British Vegetation, by Tansley (Camb. Univ. 

 Press). 



Biology of Season and of Duration. 



If we attempt to sketch a general, that is a non-specialised type of 

 Flowering Plant, it would have a cylindrical upright stem, bearing 

 leaves with petiole and lamina radiating out on all sides of it, and with 

 axillary branches repeating the characters of the main shoot. Its 

 root-system would consist of a tap-root and lateral roots of successive 

 orders, all fibrous. A young Sycamore or Apple-tree would answer 

 this general description. Further, it seems probable that the perennial 

 state was prevalent, or even constant among early Vascular Plants. 

 For it is seen almost exclusively in living Pteridophytes and Gymno- 

 sperms, and it is characteristic of the early fossils. So that in this 

 respect, as also in their general form, an Apple or a Sycamore may be 

 held as representing a type of vegetative construction usual for early 

 Flowering Plants. 



In one marked feature, however, the Sycamore and the Apple are cer- 

 tainly adaptive. Both are deciduous, that is they drop their leaves in 

 autumn, as do most of our British trees and shrubs. Leaf-fall is clearly 

 related to season. It brings the biological advantage of reducing the 

 transpiring area at the time of low temperature, when the activity of 

 the roots in the cold soil declines. It is in fact a provision against 

 what may be called physiological drought, for the roots in the cold soil in 

 winter are unable to make up for any great loss of water by transpira- 

 tion. But many familiar plants retain their leaves during the winter, 

 as " evergreens." They are mostly shrubs with leathery leaves, and 

 many of them have been introduced from southern lands, such as the 

 Rhododendron and Cherry-Laurel, from the Levant ; but Holly, and 

 Yew, and Ivy are native evergreens. 



The evergreen state is more common in plants of lands where the seasons 

 are equable, and it is probably a primitive state, while the deciduous habit 



