BULLETIN NO. 30. 
The largest genus of summer-flowering trees here is Tilia, the Lindens, 
which are now at the height of their flowering time although the flowers 
of a few of the species are already fading and those of some others are 
just opening. The genus is widely and generally distributed in all the 
temperate parts of the northern hemisphere with the exception of west- 
ern North America and the Himalayas. Between forty and fifty species 
and several hybrids are recognized, for hybrids and supposed hybrids in 
Tilia are common, and among these hybrids are some of the handsomest 
and most rapid-growing of all Lindens. Although Lindens are much 
planted for the embellishment of parks and as street trees there is great 
confusion, especially in the United States, in regard to the different 
forms which are cultivated, and this confusion in so far as it relates to 
the European species was imported from Europe with the trees, for 
Linnaeus and many botanists after him believed that the Lindens of 
northern and western Europe were only forms of one tree, and so started 
the trouble. 
In eastern North America there are seven species of Linden trees; 
four of these are from the extreme south and either are not hardy in the 
Arboretum or have been tried here during such a short' time that they 
need not now be considered. The Linden of the north, T. americana, is 
a splendid great tree growing to its largest size on rich hillsides and 
moist bottom-lands, and showing its greatest beauty in the forests of 
New Brunswick, northern New England, and the valley of the St. Law- 
rence River. This tree may be easily distinguished from the other Lin- 
dens by the green and shining lower surface of the leaves which has no 
hairy covering with the exception of rather conspicuous tufts in the axils 
of the principal veins. This tree has been somewhat planted in eastern 
Massachusetts but less frequently than in the neighborhood of more 
northern cities. Here, especially in dry summers, the leaves are some- 
times made brown by the red spider which, however, is easily controlled 
by spraying. Tilia spectabilis, which is believed to be a hybrid between 
this tree and Tilia tomentosa of eastern Europe, is a very vigorous and 
fast-growing tree of much promise. In some European nurseries it is 
sold under the name of Tilia Moltki. Tilia Jlavescens, usually found in 
nurseries under the name of T. Jloribunda, is a supposed hybrid between 
T. americana and the European T. cordata. This tree is remarkable in 
its rather small, thick and very lustrous leaves, and large flowers. 
Plants only a few feet high flower profusely. 
The second North American Linden tree, T. alba , or, as it is often 
called, T. Michauxii, although it was first distinguished and made known 
nearly a century ago, was long overlooked or misunderstood by botanists; 
and it is only in recent years that this handsome tree has been found to 
be widely distributed from the valley of the St. Lawrence River to 
Georgia and Arkansas. It may be distinguished from T. americana by 
the pale lower surface of the leaves, which is more or less covered with 
star-shaped clusters of white hairs. This tree is now well established in 
the Arboretum, although the plants are not old enough to flower. 
The third of our northern Lindens, T. heterophylla, is a species of the 
Appalachian Mountains and is distributed from western New York to 
northern Alabama, and through Kentucky to southern Indiana and Illi- 
nois, growing to its greatest beauty and to its largest size in the forests 
which cover the slopes of the mountains of North Carolina and Tennessee. 
