8o Studies in Forestry [CHAP. iv. 



fail to be noted from the above that long-needled Pines 

 transpire more freely than the true Firs having short foliage. 

 But in the conifers (which, as has been previously remarked, 

 require only about \ to -$ as much water as broad-leaved 

 trees) the rate of transpiration is limited very considerably by 

 their thick, strongly-cuticularized epidermis impregnated with 

 resin and wax. Hence, not only the rate of transpiration, but 

 also the movement of the sap upwards within conifers is much 

 more sluggish than in deciduous trees like the Oak, Ash, Elm, 

 &c. And whilst the needles, with their weaker transpiratory 

 capacity, contain as much water as the leaves of many kinds of 

 deciduous trees, the woody tissue of conifers contains more 

 water than that of the latter. 



The Indispensable Mineral Ingredients in the food- 

 supplies of plants comprise Potash, Lime, Magnesia, Iron, 

 Sulphur, and Phosphorus as well as Nitrogen. And at the 

 same time Silica (often in large quantities), Chlorine, Soda, 

 Manganese, and occasionally Alumina, are also to be found in 

 the ashes of timber, after Carbon, Hydrogen, Oxygen, and 

 Nitrogen have been eliminated by combustion ; but the former 

 can hardly be considered indispensable constituents. The 

 different uses to which these mineral substances are put in the 

 vegetable economy have not yet been quite satisfactorily 

 determined. Potash (K 2 O) is found chiefly in the foliage 

 and the parts of more recent growth, which are concerned 

 with the active processes of assimilation and of vital ac- 

 tivity. Lime (CaO) is supposed to play a very important 

 part in connexion with the formation and distribution of 

 the carbo-hydrates, and in the formation of insoluble com- 

 pounds with oxalic and similar injurious acids which are 

 thus rendered harmless to the tender tissues of the plant. 

 Whilst Beech and Black Pines show a decided preference for 

 soils rich in lime, it has been proved by Fliche that even 

 a slight percentage of carbonate of lime seems to act as 

 a poison in the case of the Sweet Chestnut and the Maritime 



