422 BOTANICAL GAZETTE [NOVEMBER 
slightly in size, is always globose, depressed-globose, slightly ovoid, 
or ellipsoidal, fruits of these different forms occurring in the same 
species and some of them on the same tree. The shape and size 
of the leaves vary on different branches of the same tree, but 
their serration and venation have sometimes: specific impor- 
tance. The only constant and reliable character, however, which I 
have found for distinguishing the species is in the absence or 
presence of the hairy covering on the surface of the leaves and in 
the nature of this covering when it exists, and the following 
arrangement of the species is based on these characters. The 
color of the hairs, however, cannot be depended on; on some species 
the hairs on the lower surface of the leaves are constantly white, but 
in other species they are brown or white on different trees, and on 
others they are white on the leaves of lower branches and brown on 
those of upper branches. When it is possible to make a compara- 
tive study of the trees growing together in an aboretum where 
they can be watched through the year it will probably be found 
that some of the characters which now seem constant cannot be 
depended on and that another arrangement of this group will be 
necessary. 
Unfortunately the lindens first known from North America 
were described in Europe, often from cultivated trees, and the 
material on which these descriptions were made was insufficient 
and is often no longer in existence. There is therefore still some 
uncertainty in regard to the correct names of a few species. 
I take this opportunity to express my sincere thanks to Mr. T&. 
HARBISON, Professor R. S. Cocks, and Mr. E. J. PALMER, who have 
patiently and industriously collected Tilia material for the Arbo- 
retum and made possible these notes. 
CONSPECTUS OF THE SPECIES OF THE UNITED STATES 
Surface of the leaves glabrous at maturity 
Leaves glabrous or almost glabrous when they unfold, coarsely serrate. 
Leaves furnished with conspicuous tufts of axillary hairs, their lower sut- 
face light green and lustrous; pedicels glabrous or nearly glabrous 
1. I. gare 
Leaves usually without tufts of axillary hairs, their lower surface not 
lustrous; pedicels densely hoary tomentose. ..........-+-- 2. T. nuda 
