TOUW GARDEN ON GRAVEL. 



43 



lilacs in variety, giieldre roses (snowball tree), ribes (tlowering currants), Forsytliia 

 suspensa, Spira?a ariocfolia, weigelias, hypericums; while elders green, golden, and 

 variegated, grow in positions wliere most other kinds fail. Deciduous trees and shrubs 

 succeed better than evergreens under a canoj)y of smoke, because the former cast the 

 whole of their leaves at once in the autumn, and produce new leaves (breathing organs, 

 etc.) in the spring {sec page 19). 



Fig. 26. Town Garden, on Geavel. 



EvERGEEENS, SO Called because they retain their leaves in winter ; but they cast 

 them all the same, though gradually, during the spring and summer. In this respect 

 they possess an advantage in smoky districts over coniferous trees, such as cedars, 

 cypresses, and the like, also yews, which do not renew their "leaves" annually, as 

 these are scaly extensions of the bark which hold sooty particles, and hence the trees 

 do not thrive where smoke prevails. 



CoxiFERS. — There is one conifer, the deciduous cypress (Taxodium distichum), that 



G 2 



