NO. I 
Complimentary 
NEW SERIES VOL. VII 
ARNOLD ARBORETUM 
HARVARD UNIVERSITY 
BULLETIN 
OF 
POPULAR INFORMATION 
JAMAICA PLAIN, MASS. APRIL 11. 1921 
An early spring. An unusually mild winter during which a temper- 
ature of zero was recorded only twice at the Arboretum, followed by 
a March with a temperature of 80° on two days, and an unprecedented 
high average for the month, has caused many plants to flower earlier 
than they have flowered here before. On March 21 Cornus mas, Dir- 
ca palustris, Prunus Davidiana and Acer ruhrum were in full flower. 
Rhododendron dahuricum and R. m-ucronulatum were opening their 
first buds, and on March 26 the first flowers on several of the For- 
sythias and on Magnolia stellata had opened, several Currants and 
Gooseberries were in bloom, and Corylopsis Gotoana was opening its 
innumerable flower-buds. The Silver Maple {Acer saccharinum) had 
flowered on the 9th of March, only eight days earlier than in 1920, 
although in the severe winter of 1918-19 it was in bloom in the Arbor- 
etum on the 28th of February. In earlier years Cornus mas has flow- 
ered usually as early as April 3 and as late as April 25, In the six 
years from 1914-1920 Dirca palustris which, with the exception of two 
or three Willows, is the first North American shrub to bloom in the 
Arboretum, began to flower as early as April 3 and as late as April 15. 
The fact that the winter flowering Witch Hazels bloom later in mild 
winters than they do in exceptionally cold winters is not easy to ex- 
plain. In the cold winter of 1915-16, and 1918-19, Hamamelis mollis 
was in full flower on January 26 and February 9. In 1916 Hamamelis 
japonica was in flower on January 26 and in 1919 the flowers were 
fully open during the first week in February. This year the flowers 
on these two plants did not open until the first week of March. On 
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