56 
T. petiolaris. It is a fast growing tree with leaves as large or larger 
than those of its American parent but silvery white on the lower sur- 
face like those of T petiolaris. What is believed to be a variety of 
this hybrid(var. Moltkei) originated many years ago at the Spaeth Nur- 
sery near Berlin. It is a tree of denser habit and greener leaves than 
T. spectabilis, and in the Arboretum it is a handsomer and faster-grow- 
ing tree than the native species. 
Heather. Of the true Heaths only the red and white-flowered forms 
of Erica carnea are perfectly hardy here. This is a native of the 
mountains of central Europe, and an evergreen plant only a few inches 
high which spreads gradually into a broad mat. It is one of the first 
plants to flower in the Arboretum, and this year was in full bloom on 
the 15th of March. This is one of the best small evergreen shrubs for 
a sunny Massachusetts rockery. Erica tetralix and E. vagans, two 
handsome European species, have sometimes lived for two or three years 
at a time in the Arboretum, but have not proved very hardy in any of 
the positions where they have been planted. The Arboretum two years 
ago established in its propagating department at the corner of Centre 
and Prince Streets a collection of dwarf shrubs planted in frames and 
protected from the heat of the summer sun by lath shades raised high 
enough to permit a person to walk under them and to insure a free cir- 
culation of air. In these frames it has been found possible to grow 
successfully a number of shrubs which require partial shade and daily 
summer watering, and are too small 'and often too delicate to be prop- 
erly protected in the open ground in a public garden of the size and 
character of the Arboretum. In this collection are now established such 
difficult plants as Salix herbacea and S. uva-ursi, Linnaea borealis, 
Epigaea repens, Casaiope hypnoides, Loiseleuria procumbens, Kalmia 
microphylla. Rhododendron indicum, Vaccinium praestans, and some 
three hundred other interesting dwarf shrubs which have never before 
been successfully cultivated in the Arboretum. In this collection it is 
now believed possible to maintain Erica tetralix, E. vagaris and pos- 
sibly other dwarf species, and here will probably grow the so-called 
Irish Heath {Daboecia) which has not yet proved hardy here. The 
Heather (CalLuna) is fortunately hardy in nearly all its forms, and an 
important plant for the New England summer garden or to naturalize 
in open New England woods. There is a good collection of these varieties 
of Calluna in the Shrub Collection. The first of them to flower this 
year (var. rubra) with gray leaves and crimson flowers is already in 
full bloom. The flowers of some of the white-flowered forms, of which 
there are several, are beginning to open, and now for several weeks 
the Calluna-collection will be an interesting feature of the Shrub-Col- 
lection. These plants in their compact habit and abundant bloom show 
the advantage of a severe pruning of the old wood in early spring be- 
fore the plants start to grow. Unless this is done they become thin 
and bare, and are often short-lived. Calluna should be planted in not 
too rich, thoroughly drained soil and in full exposure to the sun. 
The next of these Bulletins will appear during the month of August. 
