564 ZONES AND REGIONS [Pt. Ill, Sect. II 



photic ration. The axes of the herbs are elongated, their leaves are thin 

 and delicate ; their dark green colour is partly owing to the fact that their 

 chlorophyll is not decomposed, partly to its presence in the epidermis. The 

 large intercellular spaces of the mesophyll, the thin cuticle, the numerous 

 stomata, all denote great atmospheric humidity. 



iii. THE CONIFEROUS FOREST. 



The evergreen summer-forest, which always consists of coniferous 

 trees, possesses, in accordance with the weaker illumination of the 

 ground, a still poorer and more uniform subsidiary vegetation than 

 does the broad-leaved forest. The leaf-canopy, however, absorbs daylight 

 to a somewhat less extent than does the broad-leaved canopy of crowns 

 of the beeches and oaks ; but the bright period of spring, which is bene- 

 ficial to the vegetation on the ground, is wanting in coniferous forest. 

 Owing to this alternation, many plants seem more accommodating as 

 regards illumination when they are in the broad-leaved forest than when in 

 the coniferous forest, where the screen weakening the light is more penetrable, 

 but is always present. Thus Wiesner found Hepatica triloba close to the 

 base of a beech-trunk under a light-intensity of j Tt whilst in a forest of Scots 

 pine it does not occur under j Y ; this is a consequence of the circumstance 

 that during spring the shade of the trunk of the beech is ±, instead of ^ as 

 in summer. 



In other respects the preceding remarks regarding the shade-vegetation 

 of broad-leaved forest may be applied to coniferous forest \ 



Coniferous trees are essentially distinguished oecologically from summer- 

 green broad-leaved trees, by the xerophilous structure and consequently 

 the lesser transpiration of their leaves 2 . Yet it is by no means admissible 

 to include them among xerophytes, as Warming has done. The term 

 xerophyte may to a certain extent apply to several species of Pinus and 

 of Juniperus of dry, sandy, and stony soils, where xerophily is determined 

 by edaphic influences ; but it does not apply to most species of Abies and 

 Picea, our silver-fir and spruce for instance, which require as much moisture 

 as broad-leaved trees, and are tropophilous in the whole of their mode of 

 life. Moreover the young shoots, in contrast with those of true xerophytes, 

 have only weak protective devices against transpiration. 



It has already been stated that the xerophilous structure of conifers is 

 an hereditary character, that does not always appear to correspond with the 

 present conditions of existence of the Coniferae. This statement, however, 

 really concerns only certain places in the tropics, such as Java and Sumatra. 



1 Numerous details will be found in the special illustrations ; see next page. 



2 See p. 165. 



