1904] BILLINGS—TILLANDSIA USN EOIDES. 115 
basal cells undergo thickening of their walls in certain portions and 
lose their cell contents. 
SCHIMPER (1) was the first to call attention to the water absorptive 
function of the scales, and his experiments along this line were so 
complete as to leave little else to be done. That the leaves of 
Tillandsia can absorb water is easily demonstrated either by wetting 
them with water and then watching it disappear, or by noting the 
weight before and after allowing them to remain a short time in water. 
That the channel of absorption is through the scales is shown by using 
colored water, which stains the stalk cells. Unlike most similar 
appendages of the epidermis, the scales do not hinder the leaf from 
becoming wet, but actually conduct water into the interstices beneath 
them. When dry, the leaf is of a gray color, due to the air enclosed 
by the scales, but when wet, the air is replaced by water, and a deep 
green color results. From an examination of fig. 70 it will be seen 
that the outer walls of the scale are thickened. When water is 
absorbed by the cells with thickened walls, they become turgid, 
expand below, and raise the wing of the scale well above the epider- 
mis (jig. 69). The water absorbed by the outer cells of the scale 
passes to the stalk cells, which have thin walls and rich protoplasmic 
contents. Through these it passes through the basal cell to the water- 
storage cells of the parenchyma. If the plant be soaked in dilute 
potassium iodid solution for a day, the walls of the stalk, basal, and 
neighboring parenchyma cells will be stained. It should be noticed 
that no ordinary type of epidermal cell with its thickened cuticularized 
wall separates the scale from the parenchyma. The cell that repre- 
sents the epidermis beneath the scale is the basal cell resulting from 
the first division of the epidermal cell that gave rise to the scale. The 
walls of this basal cell are thin and uncuticularized. If a scale whose 
wing is raised well above the epidermis by the turgescence of its cells 
be treated with glycerin, the contraction due to loss of turgescence 
will draw the scale close down against the epidermis. This illus- 
trates the process that takes place when scales become dry from 
evaporation, as occurs in nature. Such a process cannot but assist 
the epidermis in checking transpiration, so that the scales may be 
considered not only as organs of absorption, but as serving to prevent 
too rapid escape of the water they have been instrumental in bring- 
ing into the plant. 
