54 FORESTS, WOODS, AND TREES 
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, Huonymus 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 
Llee Hodginsu, I, Mundyi, I. Wilson, I. nigricans, and 
I. camelliaefolia. In seaside towns one of the most, useful 
trees is the evergreen oak (Quercus Ilex), which is excellent 
as a wind-screen. 
Searcely 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 
2Aeh 
Fic. 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 
