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between its meshes to the epidermal surface which is 

 thin-walled and therefore better adapted to take up 

 water than the ordinary leaf surface. 



The other type of hair described as belonging to this 

 class is represented by Tilia alba Ait., pubescens Ait. 

 and argentea D. C. The epidermal cell here divides into 

 several which grow into horns or branches spreading 

 themselves horizontally over the leaf surface. In these 

 three cases the horns contain thin air or watery vapor. 

 Experiments in regard to absorption were made but the 

 results are of little value owing to the peculiar texture 

 of the leaf, its stiffners not being materially affected by 

 the loss of water. Here as with Populus, owing to the 

 height to which the tree grows, the amount of water 

 which is obtained from dew is probably much less than 

 in case of those plants whose leaves are spread out near 

 the ground. 



In Tilia argentea D. C. a peculiarity occurs which 

 may be mentioned here, though perhaps it has no parti- 

 cular bearing on the function of the hair. This tree 

 has been introduced in Zurich in large numbers as a shade 

 and ornamental tree for the streets. The leaves growing 

 on and toward the end of the upper outside branches 

 are turned from the ordinary leaf position by the twisting 

 of the petiole where it joins the stem, so that the under 

 gray-filzig surface is exposed to the sun and rain, while 

 the upper side is shielded. It was found on examining 

 a large tree of this species, standing on a side hill in the 

 botanical garden, that on all the inside branches, and 

 those growing next the bank so as to be shaded by it, 

 the leaves grew straight and normal; on the outside 

 branches which were more exposed to the sun and rain, 



