Complimentary 
NEW SEF<IES VOL. X 
NO. 8 
ARNOLD ARBORETUM 
HARVARD UNIVERSITY 
BULLETIN 
OF 
POPUI-AR INFORMATION 
JAMAICA PLAIN, MASS. JUNE 18. 1924 
Kverijreen Rhododendrons. The plants called Rhododendrons which 
have been chiefly cultivated in Massachusetts during the past fifty or 
sixty years have been imported from England, where they have been 
immensely popular, and are usually called “Catawbiense Hybrids.” 
They are hybrids of the Appalachian R. catawbiense which is perfectly 
hardy in New England, with handsome foliage and rather unattractive 
pale purple flowers, and primarily with the scarlet-flowered Himalayan 
R. arbor escens. Hundreds at least of these hybrids and varieties have 
been raised in Europe and many can be grown in this region. They 
require, however, specially prepared soil, frequent and copious water- 
ing, mulching with leaves, and spraying to protect them from the 
attacks of the lace-leaf fly which left to itself turns the leaves brown 
and finally kills them. The plants are all grafted, and the only Rhodo- 
dendron which has yet been successfully tried for this purpose is R. 
ponticum of the Black Sea region which is not hardy in New England. 
The wood of the two large-growing eastern American species which 
should be the natural stock for these hybrids is not available for this 
purpose as it is too hard. Some of these hybrids if well taken care of 
here live for many years, but die sooner or later owing, it is now be- 
lieved, to the tenderness of the stock on which they have been grafted. 
It looks now as if plants obtained by layering branches of the plants 
grafted on R. ponticum would be the only way to secure permanent 
plants of the Catawbiense Hybrids. As it is there are no shrubs on 
which so much money has been spent in New England with such 
meagre and unsatisfactory results. The handsomest species of Rhodo- 
dendron flowering in the Arboretum is the Caucasian R. Smirnowv, 
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