1904] BILLINGS—TILLANDSIA USNEOIDES IO! 
is found more frequently on deciduous than on evergreen trees, . 
because, as he explains, the foliage of the evergreen trees interferes 
with its reaching the branches. The umbrella tree (Melia Azederach) 
has a remarkably dense foliage and is almost universally devoid of 
moss, yet near the university is a tree of this species with a scanty 
supply of foliage and an abundance of moss. It is reasonable to con- 
clude that any tree furnishing proper conditions for attachment and 
growth may become a host of the epiphyte. 
The source of the water supply of Tillandsia is atmospheric pre- 
cipitation, as in all epiphytes. Dissolved in the water are the neces- 
sary salts which have been dissolved by the rain from the dust in the 
air. Perhaps an equally fruitful source of salts is in many cases the 
washings from the tree, which in dry weather may accumulate much 
earthy material in the form of dust upon its branches. The plant 
itself even serves in collecting dust on account of the scaly surface, so 
that when wet the deposits beneath the scales yield a small amount 
of soluble material. 
A most remarkable characteristic of Tillandsia is its ability to 
retain water. The absorption of water is accomplished over the 
entire surface of the living parts by means of scales, as will be described 
further on, its retention being accomplished also by the scales, and of 
course by the cuticularized epidermis. It is much easier to under- 
stand how a melon cactus with its globose form and consequent 
minimum surface and enormously developed water-storage tissue 
can resist prolonged drouth than it is to see how Tillandsia with its 
small cylindrical leaves, much greater surface exposure, and compara- 
tively small storage facility can, without any water supply, endure 
drouth. A small festoon was hung in a closed dry room for nineteen 
days without water. It lost 23 per cent. in weight during the time, 
but when placed in water it absorbed as much as it had lost, and 
remained a healthy plant, showing that it had not really suffered 
injury by exposure to the drouth. There is occasionally, of course, 
a similar drying process in the open air when drouth occurs. During 
the dry spell in the spring of 1902, moss plants were known to have 
been subjected to two months of rainless exposure without injury. 
From an economic standpoint, Tillandsia is of some commercial 
value on account of its mechanical tissue. This forms a central 
