NOTES ON NORTH AMERICAN TREES. III. TILIA. I 
C.-S. SARGENT 
The results of a study of the lindens of the United States carried 
on for a number of years will be found in these notes. It is based 
on observations of these trees in the forest and the examination of 
a large collection of herbarium material gathered in all parts of the 
country where lindens grow. 
To understand a species of Tilia properly 4 collections are 
needed: the first made in early spring to show the unfolding leaves, 
the second in early summer when the trees are in flower, the third 
6 or 8 weeks later when the fruit is mature, and the fourth in winter 
for the winter buds. Many of these trees grow in regions where 
summer collecting presents many difficulties and causes much dis- 
comfort; the trees do not always flower every year, and the fruit 
often does not mature or is destroyed in storms before it is ripe. 
It is not surprising, therefore, that American lindens are poorly 
represented in the older herbaria and that botanists depending on 
collections in herbaria. have not been able to obtain a compre- 
hensive idea of the representatives of the genus in this country. 
Even with abundant material it is difficult to find characters by 
which the different species and their varieties can be satisfactorily 
arranged. In most of the large genera of trees many of the species 
can be distinguished by the bark, but the bark of the American 
lindens varies so little that it has no value in determining species. 
The branchlets of some species are stouter than others, but stout 
and slender branchlets are often found on the same tree. Their 
color is uniform on some species, but on others varies from yellow 
or pale brown to red; on some species the branchlets are glabrous 
and on others they are pubescent, but in some species glabrous and 
pubescent branchlets are found on the same tree. In a few species 
a good character is found in the winter buds, but on other species 
the buds may be glabrous or pubescent. Except in size, there is no 
constant character in the flowers, and the fruit, although it varies 
421] {Botanical Gazette, vol. 66 
