54 



FOEESTS, WOODS, AND TEEES 



beautiful tints in autumn, is worthy of trial in parks and 

 gardens. 



As mentioned above, scarcely any evergreen tree can 

 be recommended for planting in the smoky areas of large 

 towns. Of the smaller broad-leaved evergreen trees and 

 shrubs, that is, those which do not belong to the conifers, 

 the most resistant to the evil conditions of towns are 

 probably box, Enonymus and Aucuba. If hollies are to be 

 planted, it is decidedly of advantage to select the vigorous 

 large-leaved kinds, which are of hybrid origin, such as 

 Hex Hodginsii, I. Mundyi, I. Wihoni, I. nigricans, and 

 /. camelliaefolia. In seaside towns one of the most, useful 

 trees is the evergreen oak (Quercns Ilex), which is excellent 

 as a wind-screen. 



Scarcely any conifer will succeed in the interior of a 

 smoky town, the most resistant being probably the Austrian 

 and Corsican pines, which have also the merit of with- 

 standing wind well and of thriving in most soils. Conifers 

 appear to be more sensitive than other plants to smoke 

 or dust. This is due to their leaves having peculiar sunk 

 stomatic openings which are designed to check transpiration, 

 but form efficient traps for particles of soot or dust. It is 



Fig. 6. — Stoma of leaf of Silver Fir, showing deposit of soot. 

 (From Cohen and Ruston, Smoke.) 



by means of the stomatic openings that the gaseous inter- 

 changes take place in the leaf; and if these openings are 

 blocked, the assimilation of carbon dioxide from the air is 

 stopped and the plant is no longer able to obtain food. 

 Conifers may occasionally be useful in town parks in 



