96 NATURAL SCIENCE. Aug.. 



These Stahl calls " Trdufelspitzen," or dropping-points, and the 

 rapidity with which tropical plants shed the rain-drops by this means 

 is very astonishing. In a comparatively moist atmosphere, after a 

 heavy rain, such plants as Ficus acuminata, Angiopteris evecta, and many 

 others possessing Trdufelspitzen had been long dry, while European 

 or Australian forms with leaves ending in blunt tips, as the Oak, 

 Apple, Eucalyptus, etc., yielded on shaking them a heavy shower of 

 drops. 



It is instructive to glance over any monograph of tropical genera 

 and note the frequent use of the terms, ^^ folia longe acuminata,'" '■^ folia 

 acuniinatissima," "folia caudata acuminata,'' These Trdufelspitzen occur 

 also on the lobes of divided leaves, and on the pinnae of compound 

 leaves, but they are, perhaps, most remarkable on entire ovate leaves, 

 such as those of Ficus religiosa, where the midrib grows out into a 

 linear point sometimes 75 mm. long, the leaf itself measuring about 

 100 mm. from the stalk to the base of the point. In some plants the 

 prolonged midrib of the leaf is a fairly wide channel, but the most 

 ordinary form is that of a tapering narrow point slightly bent back 

 and curved at the end, a peculiarity which is found in many European 

 species. As the water trickles down the inclined narrow points, it 

 passes from the upper to the under surface before dropping from the 

 leaf, and the bent tip accelerates this action very distinctly. 



Stahl tried several experiments to test this theory as to the 

 advantage of Trdufelspitzen to the plant. He took six leaves of 

 Justicia picta, one of the Acanthaceae, with leaf points a centimetre long, 

 and slightly bent at the tip. From three of these the points were cut, 

 and the ends carefully rounded ; they were then fixed on a board, 

 which was placed at an angle of 30 degrees, and sprinkled with water. 

 The rounded leaves he found retained some of the moisture for an 

 hour, the others were quite dry in 20 minutes or less. The same 

 results were obtained with other similar leaves. 



The veins of the leaf play a very important part in the drainage 

 of water from the surface, especially when they are deep-seated, or, 

 as in the Melastomacean type, where the parallel veins bend in 

 towards the apex. In plants the leaves of which slant towards 

 the stem, the water flows in a centripetal direction, and there 

 we find such contrivances as the rows of hairs in the Bird's 

 Eye [Verenica chamcsdrys), which act by capillarity like blotting paper, 

 and draw away the water from the leaf-surface. Many plants 

 with similar rows of hairs have also deep nerves and channelled 

 stems, as the Blind Nettle [Lamiiim album), Hop, etc. Kerner, 

 in his Pfianzenleben, vol. i., p. 85, discusses the importance to 

 the plant of the direction in which the water is conveyed down 

 by the leaves. He considers that it is directly related to the 

 position of the roots, and that the object is to supply moisture to the 

 young growing rootlets. But this seems hardly necessary in the case 

 of tropical plants. It seems more probable that the advantage gained 



