( 309 ) 
one sees in their natural condition at night or in the morning the 
formation of a certain number 6f drops of water on the leaves, 
a part of these drops have passed out independently of the direct 
influence of root-pressure. 
The phenomenon of guttation may be regarded as the formation, 
under certain external conditions, of drops of water at the tip and 
the margin of the leaf, whether from the water-pores as a direct 
consequence of root-pressure, or as a result of the activity of inter¬ 
nally situated glands. Further investigation of water-secretion has 
shown me, however, that this phenomenon of guttation only gives a 
very incomplete idea of what water-secretion in the plant may be 
considered to be. 
There are numerous plants which do not show proper drop-for¬ 
mation, but which nevertheless continually secrete at their surface 
fairly considerable quantities of water or watery mucilage espe¬ 
cially in their younger parts. 
It may be remembered that Treub l ) showed more than 20 years 
ago, that there is another kind of water-secretion in plants, by epider¬ 
mal trichbraes. 
Treub found that the flower-buds of a tropical Bignoniacea, 
Spathodea campanulata always contain water which is most probably 
secreted from the cushion-shaped trichomes, which cover the inside 
of the calyx in large numbers. 
Afterwards, as is well known, the same phenomenon i. e. secretion 
of water in a closed flowerbud, was observed in other tropical 
plants; in these cases similar trichomes were always observed, whether 
only on the inner surface of the calyx or also on the outer surface 
of the corolla, and there was every reason to assume that the fluid 
was secreted by these epidermal trichomes. 
For a long time this phenomenon was considered a thing apart. 
There was no inducement to connect this secretion of water inside 
the flower with that outside on the leaves. It was regarded as a 
special contrivance, a useful adaptation, brought about by natural 
selection in order to protect the ypung floral parts inside the calyx 
against too strong transpiration. 
A few years after Treub’s paper, Haberlandt, however, discovered 
that such a water-secretion, resulting from the secretory action of 
externally situated glands, can also be observed outside the flower. 
During his stay at Buitenzorg he found on the surface of the leaves 
l ) Treub M. Annales du Jardin botanique de Buitenzorg. Vol. VIII. 1890. 
