220 THE UNIVERSITY SCIENCE BULLETIN. 



The shoots of young plants, each bearing from four to five 

 leaves, were cut off, the cut surface sealed with wax and the shoots 

 allowed to dry for an hour or more. These were then weighed 

 separately and placed in a saturated atmosphere to see if they 

 would regain their turgor or gain in weight. One set was left 

 standing for forty hours, and then, after the leaf surfaces had been' 

 dried with filter paper, they were weighed. Those placed in the 

 saturated atmosphere gained 15.11 per cent in weight, while those 

 painted with distilled water and then placed in saturated atmos- 

 phere gained 18.95 per cent in weight. Another set was allowed 

 to dry for three hours and was then brushed over with distilled 

 water. The average of these tests showed a gain of 19.46 per cent 

 in two hours. This shows that the plant has some power to ab- 

 sorb moisture from the atmosphere, especially if dew is present. 

 Haberlandt ('14) gives two examples. Convolvulus cneorum and 

 Centaur ea argentea, where water is absorbed by hairs of the leaf. 

 The wilted leaves gained 10 and 13 per cent, respectively, when 

 immersed for twenty-four hours. In comparing the percentage 

 gained and the conditions of the experiment, Abutilon theophrasti 

 is much more efficient. 



The leaf is dorsiventral, with the palisade tissue a single layer 

 of cells on the upper side. Large thin-walled water-storage cells 

 over the smaller veins interrupt this layer (fig. 1, d). Both sur- 

 faces of the leaf are thickly covered with four types of hairs, 

 namely, two types of clothing hairs, one of which is stellate and 

 the other an unbranched single-celled form, and two types of 

 glandular hairs, one long and the other short. The stellate hairs, 

 the most characteristic for the family, are the common clothing 

 hairs, and these are found in great numbers and almost exclusively 

 over the veins. The rays of the stellate hairs vary in number and 

 length. They are united at their bases in the plane of the epider- 

 mis; and there being no stalk cells, these hairs do not rise far 

 above the epidermal surface. The walls of the basal portion are 

 relatively thick and contain pits (fig. 6). A ray cell (fig. 5) has 

 the cavity diminishing toward the apex until in some cases it is 

 entirely closed there. The walls of the rays show up as being 

 composed of two layers — a thin outer cuticle imperfectly developed 

 and a thick inner portion which the chloroiodide of zinc test gave 

 evidence of being slightly infiltrated with cutin. The basal por- 

 tion of these hairs stain a bright red with safranin, and yellow 

 with chloroiodide of zinc, indicating cutinization, or possibly 

 lignification ; but give no color reaction with phloroglucin or ani- 



