SECTION XV 

 CLASS XII. CONIFEROUS FORMATIONS. FOREST 



CHAPTER LXXXVI. EVERGREEN CONIFERAE 



The scale-like leaves of the Cupressaceae and the needles of the Abie- 

 taceae are representative of coniferous foliage, which is characterized by 

 smallness of surface, strong cuticularization of the epidermis, frequent 

 sunken position of the stomata, and other features calculated to depress 

 transpiration. Evergreen, coniferous trees exhale much less water-vapour 

 than dicotylous trees, but the amount of transpiration varies with the 

 species.^ In accordance with their xerophytic nature conifers have few 

 or insignificant root-hairs. 



Evergreen Coniferae are pronounced xerophytes when judged by 

 their morphology, anatomy, and physiological characters. The reason 

 why they are not grouped together with sclerophyllous vegetation, but 

 are dealt with here in a separate section, is that sclerophyllous formations 

 constitute a natural group adapted to definite climatic conditions, namely, 

 to a subtropical climate where the rain falls in winter. As characteristic 

 peculiarities of sclerophyllous Dicotyledones we may regard, in addition 

 to the small size of the leaf, the rarity of arboreous growth and the normal 

 absence of bud-scales. 



Coniferous forest occurs in the most diverse climates, which, however, 

 do not include the torrid dry climate. It is most extensively distributed 

 in the cold-temperate zone of the Northern Hemisphere, and becomes 

 less prominent in warmer climates. 



The soil upon which coniferous forest occurs varies widely, yet, so far 

 as reliable information is available, it is always physically or physiologically 

 dry a fact that harmonizes with the xerophytic structure of Coniferae. 

 In warmer regions coniferous forest has, as a rule, seized upon permeable, 

 warm, sandy soil ; but in colder places it grows upon nearly all kinds 

 of soil, varying from dry rocks and sand-fields to wet, marshy ground. 

 This accords with the evergreen nature of most Coniferae. The cold 

 winter is a physiologically dry season, against which trees can protect 

 themselves by defoliation or by xerophytic structure. The larger plants 

 that have to endure a severe winter, and are too tall to derive protection 

 from a covering of snow, need protective devices capable of saving them 

 from death due to lack of water in winter.^ Added to this is the circum- 

 stance that in cold regions most Coniferae produce raw humus and 

 therefore an acid, physiologically dry soil. 



The xerophytic structure of Coniferae is, as M. C. Stopes ^ has pointed 

 out, a phyletic character. Her suggestion is that the xerophytism of 

 the Coniferae is a result of the imperfect nature of the water-conducting 



^ See M. C. Stopes, 1907. * Schimper, 1898. * M. C. Stopes, loc. cit. 



