27 6 THE MOVEMENTS OF IV ATE R 



bolus *. The pseudo-parenchymatous mycelia of many fungi often excrete 

 large quantities of fluid, which in certain cases at least contains very little 

 dissolved substances. Merulius lacrymans, several species of Polyporns, 

 Nyctalis, &c., the growing ends of the mycelial strands of Hypoxylon 

 carpophilum, and the scelerotia of certain species of Coprinus and Peziza 

 all have this power. The sugary fluid which may escape from the 

 conidium stage of Claviceps purpnrea is probably excreted in a similar 

 manner to -that in nectaries. 



The power of excreting water appears often to be present in sub- 

 terranean organs as well, as is no doubt the case in root -hairs ; accord- 

 ing to Darwin, the scale-leaves of Lathraea sqnamaria also excrete water 

 in abundance 2 . When the exudation-pressure becomes very pronounced, the 

 roots may in certain parts excrete water instead of absorbing it, and in 

 a similar manner a circulation of water may be produced in submerged 

 plants (Sect. 46). A tendency of this nature must always exist when 

 two neighbouring roots are kept immersed in solutions of different osmotic 

 strength. 



The excretion of water may serve a variety of purposes, such as to 

 bring a substance secreted by the cell into a position where its purpose 

 may be fulfilled, or where its full power may be exercised. Herein lies 

 the importance of the excretion of water in nectaries and in carnivorous 

 plants, &c., for in the former case the excretion of sugar is accelerated, 

 while in the latter an enzyme is contained in the escaping water, which 

 also facilitates the absorption of the products of digestion. In the same 

 way the excretion of water from rhizoids and root-hairs may enable 

 a special solvent influence to be exercised in some cases upon the living 

 or dead substratum, and may aid in the penetration of fungal hyphae into 

 living organisms or organized structures ; indeed it may first make such 

 penetration possible. Again, the pollen grain germinates in the fluid ex- 

 creted by the stigma, and a similar process fills the micropylar orifice with 

 a solution of the substances which attract the pollen tube to its proper 

 destination. In some plants, as for example Corsinia marchantioides*, 

 the antherozooids reach the archegonium by means of the water which the 

 plant itself excretes, although in other cases dewdrops appear to serve the 

 same function. It is possible that the water which the roots may excrete 

 may serve in some cases to soften the earth and enable the growing roots 



1 On the excretion from Fungi see Zopf, Die Pilze, 1890, p. 186 ; Brefeld, Unters. iiber Schimmel- 

 pilze, 1881, Heft 4, p. 68 ; Schmitz, Linnaea, 1843, Bd. XVII, p. 472 ; Wieler, Cohn's Beitrage, 1893, 

 Bd. vi, p. 16. 



2 Darwin, Bewegungsvermogen, 1881, p. 71 ; Haberlanclt, Jahrb. f. wiss. Bot., 1897, Bd. XXX, 

 p. 510 [Goebel, Ober d. biologische Bedeutnng d. Blatthohlen bei Toztia u. Lalhraea, Flora, 

 i.xxxm, Heft 3, 1897; Groom, Annals of Botany, Vol. XI, 1897, p. 385]. 



3 Leitgeb, Flora, 1885, p. 330. 



