OCTOBEE 11, 1895.] 



SCIENCE. 



481 



CURRENT PE0BLE3IS IN PLANT 3I0EPH0L- 



OGY(n.). 



THE INFLUENCE OF SPRAY AND EAIN ON THE 



FORMS OF LEAVES. 



The interesting work of Stahl*— based 

 upon observations made at the Buitenzorg 

 gardens, and thus indicating tropical con- 

 ditions and recording tropical results- 

 served to direct attention towards those 

 adaptive form-modifications which leaves 

 take when subjected to excessive rainfall. 

 That the points and serrations of the leaves 

 were in such cases usually prolonged and 

 slender; that the leaves frequently adopted 

 a vertically suspended position; that the 

 nerves in many cases were sunken in gul- 

 lies, thus inaking channels from which the 

 superfluous water easily escaped; that the 

 arrangement of hairs on leaves and stems 

 contributed to the ready dispersion of 

 water, were among the facts made clear in 

 this contribution. Previous students, as, 

 for example, Lundstromf and Wille,J had 

 alreadjr brought out some of these, but 

 Stahl's work is noteworthy from its novel 

 points of view as well as for its solid addi- 

 tions to the knowledge of the subject. Of 

 particular interest is his summing up of 

 the ecologic importance of rain specializa- 

 tions in tropical leaves. That it is neces- 

 sary to disburden the leaves of their weight 

 of moisture; that this superfluous water 

 must be conducted to the roots and not 

 intercepted by the crown; that the upper, 

 sides of the leaves must be freed from at- 

 tached epiphytic algte, fungi and lichens; 

 that the transpiration stream, passing with 

 difficulty from a leaf the surface of which 

 is wet, must be promoted by the rapid dry- 

 ing off of the surface, are some of the rea- 



sons brought forward to account for the 

 morphological j)eculiarities of the rain 

 leaves. 



The most peculiar single form-character 

 of the rain leaf is the elongated point or 

 ' Trckifelspitze,' and this has been shown to 

 be characteristic not only of tropical plants 

 subjected to a rainy season, but of strand 

 plants subjected to the ocean spray, of high 

 mountain and plateau j)lants subjected to 

 heavy dews and of temperate zone plants 

 where the rainfall is excessive. 



Jungner,* whose earlier researches have 

 contributed to the subject, j brings out a 

 valuable paper in which considerable direct 

 experimental work is recorded and several 

 new observations are described. The most 

 novel part of the work is the discussion of 

 the influence of cataract spray upon the 

 plants growing in the gorge beneath or be- 

 side the waterfall. ' Trdufehpitzen ' are 

 shown to characterize plants in such loca- 

 tions, and several figures showing the differ- 

 ence between normal habitat and spray 

 habitat leaf forms are given. In such an 

 habitat, too, the customary hairiness of the 

 leaf is reduced, hairs having a tendency to 

 retain the water too long, and peculiar 

 groupings of the leaves on the stem, signifi- 

 cant as arrangements for rapid draining off 

 of water, were observed. The glazing by 

 wax of the upper surface of the leaf in some 

 cases served to reduce its ' wetableness.' 



The most valuable part of the work, 

 however, is the experimental portion in 

 which it is shown how form-modifications 

 may be produced in the greenhouse by sub- 

 jecting leaves to regular dropping of water 

 or to spray. The characteristic rain forms 

 and spray forms were thus developed in a 



(*) Regenfall and Blattgestalt. Leiden, 1893. 



t Die Anpassungen der Pfianzen an Eegen und 

 Thaue, Upsala, 1884. 



t Kritische Studieu iiber die Anpassungen der 

 Pflanzen an Regeu und Thaue. Cohn's Beitr. Biol. 

 Pflanz. 4 : hft. 3. 



*Wie wirkt trauf eludes und fliessendes Wasser 

 auf die Gestaltung des Blattes ? Bibliotbeca Botan. 

 32. Stuttgart. 1895. 



t Om regnblad, daggblad ooh snoblad. Bot. 

 Notiser No. 3, 1893, No. 3, 1894, mid Klima und 

 Blatt in der Eegio alpina. Flora. 1894. 



