other species, E. japonicus and E. subsessilis, are smaller plants with 
smaller yellow flowers and are less valuable ornaments of the garden. 
Some of the most valuable shrubs now found in gardens are natural 
hybrids of related species or have been produced by skilful hybridizers. 
One of the most beautiful of Lilacs, Syringa chinensis, described in a 
recent issue, is a natural hybrid which appeared one hundred years ago 
in the Botanic Garden at Rouen. Several of the most attractive Honey- 
suckles are hybrids, and in recent years the crossing of different species 
in several genera has produced new races of garden plants which have 
vigor, hardiness and beauty not possessed by their parents. A good ex- 
ample of the value of such hybrids is found in Deutzia Lemoiriei, ob- 
tained by a French nurseryman by crossing the Japanese D. gracilis 
with D. parvijlora of northern China, and now in flower in the Shrub 
Collection. Although it resembles D. gracilis in habit, it grows into 
a taller and broader shrub; the flowers are larger and it is much hardier. 
It is certainly one of the best garden plants of recent introduction. The 
systematic crossing of shrubs with the object of creating nev/ forms, 
except perhaps in the case of Roses, is a comparatively new industry, 
but it has already produced startling results in such genera as Magnolia, 
Deutzia, Philadelphus, Ceanothus, Rhododendron, and Diervilla; and 
with the great number of new shrubs discovered in recent years in east- 
ern Asia and eastern North America at his disposal the hybridizer will 
now have new and abundant opportunity to show his judgment and skill 
in producing new races of plants. Hybrid trees are naturally less com- 
mon than hybrid shrubs and, except in the case of fruit trees, compar- 
atively few attempts to cross different species of trees have been made. 
Trees which are believed to be natural hybrids, however, are not rare. 
There are several American Oaks which are probably hybrids and these, 
so far as they have been tested in the Arboretum, grow more rapidly 
than their supposed parents. For example Ulmus vegeta, which is be- 
lieved to be a hybrid between two European species, grows more rap- 
idly than any other Elm-tree, and the so-called Carolina Poplar, which 
is not an American tree but probably a hybrid between the American 
Cottonwood and the European Black Poplar, outgrows, at least while 
young, all other Poplar trees. 
Several of the Rhododendrons in the collection at the base of Hem- 
lock Hill are in flower and the flower-buds of many others are fast 
opening. The end of this week and the beginning of next week will 
probably be the best time to visit this collection which is most easily 
reached from the South Street entrance where automobiles should be 
left. 
This is one of the most interesting times of the year to visit the 
Pinetum, for many conifers are now in their greatest beauty, as the 
young shoots, of various shades of green or blue, are now growing 
rapidly on many of these trees and often afford good characters for dis- 
tinguishing the Firs, Spruces and Pines. Particularly handsome just 
now are the Carolina Hemlock ( Tsuga caroliniana), the Colorado White 
Fir {Abies concolor ), the two Rocky Mountain Spruces ( Picea pungens 
and P. Engelmannii), now bluer than they will be later in the season, 
and the Douglas Spruce, {Pseudotsuga mucronata). An entrance to the 
Pinetum is close to the Walter Street gate. 
The Arboretum will be grateful for any publicity 
given these Bulletins. 
