20 PRESENT-DAY GARDENING 
resisting nature of their hybrids is sure to be more or less 
influenced by them. The quality of the soil that is suit- 
able for garden Rhododendrons need not be what is known 
as rich, as they certainly grow well and are happy when 
planted in a light, sandy soil over a gravel subsoil. 
The Swamp Honeysuckles are chiefly natives of north- 
eastern regions and high mountain ranges. The earliest to 
flower are R. canadensis (Rhodora) and R. nudifloruni in 
April, then R, calendulaceum and R, occidentale in May and 
June, the latest being R. arhorescens and R. viscosum, which 
are in bloom in July. They are abundant in swampy land, 
often at considerable altitudes, and when in flower they 
produce an effect of great magnificence. 
EUROPE 
It is remarkable that, although the climate and other 
conditions in many parts of Europe are specially favourable 
to Rhododendrons, only very few species are natives, and 
these chiefly in alpine regions. There are evidences in the 
Miocene rocks of Central Europe of Rhododendrons, and 
they were quite common in the Arctic regions of both 
hemispheres during the Tertiary period. The only species 
which have been able to retain a foothold in Europe are 
R, lapponicum in Norway, R. ponticum in South Spain, 
R. ferrugineum and R, hirsutum in the Swiss Alps. R. 
ponticum reappears in Asia Minor, Syria, and in the 
Southern Caucasus with R. flavum (Azalea pontica) and 
R. caucasicum, 
R, ponticum was introduced into Ghent before 1763 
and is of special interest as being the plant on which the 
genus was founded and the first to become naturalised in 
