PATH AND RATE OF TRANSFER. 259 



692. The converse of Hales's experiment is equally conclu- 

 sive. If the continuity of the wood of a stern is interrupted by 

 the removal of a short truncheon without at the same time much 

 injuring the bark, the leaves wither in a short time. Cotta l 

 asserts that upon a shoot of willow which still maintains its 

 connection witli the plant through the bark, but has had a sec- 

 tion of wood removed, the leaves will wither as quickly as they 

 would upon a shoot wholly severed from the parent plant. 



693. That water can be conveyed through the stem in a 

 direction opposite to its normal course is shown in an experi- 

 ment by Hales: " I took a large branch of an apple-tree, and 

 cemented up the transverse cut at the great end, and tied a wet 

 bladder over it ; I then cut off the main top branch where it was 

 f inch diameter, and set it thus inverted into a bottle of water. 

 In three days and two nights it imbibed and perspired four 

 pounds two ounces and one half of water, and the leaves con- 

 tinued green ; the leaves of a bough cut off the same tree at the 

 same time with this, and not set in water, had been withered 

 forty hours before." 



694. Determination of path and rate of transfer. Two modes 

 of experimenting have been employed in order to ascertain ex- 

 actly the path and the rate by which water is transferred through 

 ligneous plants. The first of these consists in using a colored 

 solution, which, when taken into the plant, tinges all the tissues 

 with which it comes directly in contact. The stem or branch 

 used in the experiment is cut sharply off and its end is plunged 

 at once into a colored solution, for instance, of some aniline 

 dye or some colored vegetable juice. As the liquid ascends the 

 stem, certain portions of the tissues become more or less deeply 

 tinged, and its course and rate of ascent can be traced by sec- 

 tions made at any given time, at different distances above the cut 

 end. A similar method has been also employed by plunging in 

 colored water the uninjured roots of the plant to be examined. 3 



1 Quoted by Pfeffer: Pflanzenphysiologie, i. 123. 



2 Statical Essays, i., 1731, p. 131. 



1 " Quel que soit le liquide employe et les variations de 1'experience, les 

 resultats generaux out pen varie, savoir : que 1'eau coloree ne penetre ni par 

 1'ecorce ni par la moelle, mais toujours au travers du corps ligneux, tantot 

 dans toute son etendue, quelquefois dans sa partie la plus jeune, savoir, 1'ex- 

 terieur du corps ligneux des exogenes, et 1'interieur des endogenes. On obtient 

 ce meme resultat general, soit qu'on plonge les plantes munies de toutes leurs 

 racines, soit qu'on emploie des branches coupees " (De Candolle's Physiologic 

 vegetale, p. 83). 



