directly connected with this fact. It apparently forms a screen 
which protects the underlying chlorophyll from the intense action of 
the tropical sun. This hypothesis is home out by the arrangement of 
the chlorophyll in the leaves of pineapples and related species of the 
same family, as will be presently shown. 
One of the peculiar features of the pineapple leaf is the apparent 
absence oi' stomata. Hundreds of sections were made from pine- 
apple leaves and examined under the microscope, and portions of the 
epidermis of the upper and under sides of the leaves were carefully 
examined without finding any true stomata. There are in some 
parts of the leaves pits in the epidermis in which much-branched 
scale-like trichomes are attached. These structures are particularly 
numerous on the under side of the leaf near the base. The trichomes 
in question are supposed to be connected with the absorption o| 
water. 
Running through the leaves parallel to the strands of fibrovascular 
tissue are strands of branched or stellate cells, which show large 
intercellular spaces between their branches. These strands lie directly 
over the pits in the epidermis of the lower side of the leaf and 
seem to be connected with transpiration and the absorption of gases. 
It would appear that the respiratory system of the pineapple is 
abortive, for when the leaves of Bromelia are studied the develop- 
ment of the strands of branched cells and the stomata is very con- 
spicuous. In this genus there are numerous small tubular masses 
of branched cells which extend from the general strands of this 
tissue to the epidermis of the lower side of the leaf and are directly 
connected with the stomata, which are arranged very close together 
in parallel furrows which alternate with ridges on the lower surface 
of the leaf. In the pineapple, on the other hand, there are no spe* 
cially modified cells connecting the strands of branched cells with 
the epidermis. In Greigia, another genus of this family, no branched 
cells occur in the leaves. The chlorophyll-bearing tissue in this 
genus is a very thin layer on the lower surface of the leaf, and the 
respiratory processes appear to go on without the assistance of the 
stellate cells. 
In cross sections of normal pineapple leaves it is at once noticed 
that from one-fifth to two-fifths of the thickness of the leaf on the? 
upper side is composed of colorless tissue containing cell sap and 
practically no other cell contents. This tissue, with the exception 
of one or two layers of cells next to the epidermis, is concerned in 
the movement and. transportation of cell sap. Below the region of 
the palisade cells lies the spongy parenchyma, which occupies about 
three-fifths of the thickness of the leaf of the pineapple, and through 
which the strands of fihrovascular tissue run lengthwise of the leaf, 
m°— BnlL 2&— 12 2 
