I. 



The Cause of tlie Excretion of Water on the Surface 



of Nectaries. 



By 

 Dr. W. P. Wilson. 



From 

 Cambridge, Massachusetts, U, S. A. 



The excretion of water on the surface of plants, containing more or 

 less solid substance in Solution, is a very common phenomenon. It may be 

 taken for granted Ihat every one at all familiär with Vegetation has ob- 

 served some of these numerous cases. 



Most plants when wounded in the spring present a flowing of water 

 from the surface of the wounded part. The grape-vine bleeds for days 

 when pruned too late in the spring. Places are often observed on the roots 

 or trunks of trees where the water continues flowing for many days together 

 on account of some slight wound. Large drops of a clear fluid are often 

 found on the tips or edges of the leaves of grass early in the morning; or in 

 the evening, when the air is nearly or quite saturated with moislure. This 

 is generally not dew, but water which has been forced by internal pressure 

 to the surface of the leaves. There are very many of our common plants 

 which when observed in a moist or saturated atmosphere, during their 

 natural period of growth, will be found to present the same phenomenon. 



This excretion of water on the teeth or tips of leaves takes place of- 

 tenest through much changed stomata, called water-pores ^) ; or rarely by 

 means of the ordinary ones 2) . 



Tropaeolum, Colocasia, Aconitum, Fuschia globosa, Musa, Brassica, 



the Grasses, Tigridia pavonia, Pilularia globulifera, 



1) De Bary, Vergleichende Anatomie 1877. p. 54. 



2) Moll, Untersuchung über Tropfenausscheidung und Injection bei Blättern. 

 Overgedruckt uit de Verslagen en Mededeeiingen der Koninklijke Akademie van We- 

 tenschappen, Afdeeling Natuurkunde 2. Keeks, Deel XV. 4 880, 



Unteranchungen ans dem botan. Institut in Tülüngen. Bd. I. 1 



