498 ORGANOLOGY. 



recent researches have shown that endosmose may exist without exos- 

 mose, and that the last is entirely dependant on the specific nature of 

 the two fluids. Further observations are needed on this subject.* 



197. The excretion of fluid substances has hitherto been but 

 very imperfectly observed. I mention by way of example the 

 following : 



1. The separation of fluid water, through cells which are filled 

 with water, and which do not impede its passage by the thickness 

 of their walls, or by an external covering which might interrupt 

 its escape in any large quantity ; e. g. the glands in the pitchers 

 of Nepenthes. Whether this water actually escapes in fluid form, 

 we know not ; but it is probable, for we find in other cells with 

 slender walls that water must escape as water, and not as vapour, 

 the proof of which is, that it carries with it and deposits a quantity 

 of matter which could not have accompanied it in the form of vapour ; 

 for instance, the crystallised sugar found in the flowers of the 

 Fritillaria and other nectaries, and the chalk upon the margin of 

 the leaves of so many species of Saxifraga. 



2. All excretions of peculiar matters on the surface of plants are 

 probably to be classed here ; for instance, the numerous clammy 

 juices on account of which we call a plant viscous (yiscosus). 



3. Related to this kind of excretion is the gradual formation 

 of a thicker or thinner layer of wax, the rime (pruina) upon the 

 surface of many plants and parts of plants, which, on account of 

 it, are designated pruinose (pruinosus), glaucous (glaucus), &c. 

 With respect, however, to this last secretion, we might, with some 

 probability, follow out its reaction upon the life of the cells, and 

 thus upon the entire plant, inasmuch as this incrustation on its 

 surface deprives the cells, yet active, of their power of exhala- 

 tion. 



4. Lastly, we may cite the excretion of the volatile oils 

 through evaporation, especially from the leaves, and sometimes the 

 flowers. 



With regard to the excretions, we are yet much in the dark. 

 Wherever a perfectly-formed epidermis exists, they only occur as the 

 result of disease ; as, for instance, the excretion of juices which are rich 

 in sugar through the leaves, called honey-dew, and the excretion of water- 

 drops in the Grasses, Aracece, in Poplars, and in Willows. There are 

 parts of plants in which no epidermis and no superficial layer of secretion 

 are present to prevent exudations ; in such parts the juices formed in the 

 cells penetrate through the membranes, and are found externally. If these 

 juices contain much solid matter, the water may evaporate from them, and 

 the solid matter may accumulate, and, if its physical properties permit, 

 may contribute to the process of exudation by endosmose. 



The separation of clear water in pitcher-formed leaves is one of the 

 most remarkable of these exudations. The fact in Nepenthes is suffi- 

 ciently established, though the observations respecting it are few. In 

 Saracenia I have never observed water in the pitchers, excepting what 



For the most recent information on this subject, see Matteucci " On the Physical 

 Phenomena of Living Beings," translated by Dr. Pereira. TRANS. 



