THE EXCRETION OF WATER FROM UNINJURED PLANTS 275 



substances. No flow of water will become apparent externally when the cells 

 which are actively or passively excreting water are deeply seated, and the 

 surrounding inactive tissue absorbs the water again as fast as it is excreted. 



Bearing in mind all these possibilities it is impossible to say whether 

 the drops of water which appear upon the sporangiophore of Pilobohis, when 

 it is kept in a saturated atmosphere, are formed by the active or the 

 plasmolytic excretion of water (Fig. 37). As a matter of fact a drop of the 

 fluid leaves a crystalline deposit when allowed to dry upon a cover slip. 

 It is therefore possible that the excretion of water is plasmolytic in this 

 case, for any osmotic substance must always tend to withdraw water from 

 a fully turgid cell with which it is in contact. 



It is, however, probable that the excretion of water into the pitcher 

 of Nepenthes is an active process although the flow may continue when 

 the plant is net fully turgid. On the other hand, the small amount of 

 material dissolved in the pitcher-fluid is quite sufficient to support a higher 

 column of water than would suffice to fill the pitcher ; still even in 

 a saturated atmosphere the pitchers are never com- 

 pletely filled 1 . Apparently either a backward filtration 

 must be possible, or else the same constant level must 

 be maintained by a regulatory influence upon the ex- 

 cretory activity exerted by the pressure. In Dionaea and 

 other carnivorous plants the excretion of water is influ- 

 enced by or dependent upon external stimuli. As we have 

 already seen (Sect. 46) the power of bleeding may be 

 similarly aroused by certain external agencies. 



The hairs both of carnivorous and other plants can 

 often excrete water. Those which occur on the leaves and FIG. 37. 

 stems of Cicer arietimim, Circaea hitctiana, Epilobium 

 hirsutum, &c., pour out an acid fluid, while in a saturated atmosphere 

 drops of water appear commonly to be excreted by most hairs and by 

 the rhizoids of Marchantia, &c. 2 Since these drops of fluid always contain 

 dissolved substances (Sect. 28) it is impossible to say whether they are 

 produced by intracellular excretion under pressure, although this appears 

 probable. On the other hand, in glandular hairs which excrete a sugary 

 fluid the process is probably similar to that which occurs in nectaries. 

 The excretion of water from Mucorineae, as well as from Penicillium and 

 other filamentous fungi, is probably similar to that exhibited by Pilo- 



1 Wunschmann, Uber die Gattung Nepenthes, 1872, pp. 25, 31 (Composition of the pitcher- 

 fluid ; Filling of pitchers on cut branches). Cf. also on the excretion of water in Cephalotus and 

 Sarracenia, Goebel, Pflanzenbiol. Schilderungen, 1893, Th. ii, p. 170; 1891, p. ito. 



2 Stahl, Pflanzen u. Schnecken, 1888, p. 42 ; de Candolle, Pflanzenphysiol. , 1833, Vol. I, p. 190. 

 On the secretory activity of the hairs of Fuchsia globosa see Gardiner, Proceedings of the Camb. Phil. 

 Soc., 1884, Vol. V, p. 39 ; Molisch, Sitzungsb. d. Wien. Akad., 1887, Bd. xcvi. Abth. i, p. 103; 

 Czapek, Jahrb. f. wiss. Bot, 1896, Bd. XXIX, p. 32:. 



T 2 



