MOVEMENT OF WATER IN PLANTS. 6oi 



by the absence of light and the cooHng of the air, and the activity of the roots 

 increased by warm damp earth. In some plants, as Nepenthes, Cephalotus &c., 

 curious pitcher-like structures occur at the ends of the leaves, at the bottom of 

 which water exudes, and in which it. collects ^ Even in unicellular plants, or those 

 whi^ch consist only of rows of cells, as the Mucorini {e. g. Pilobolus crystalliniis), 

 PemciUium glaucum, and the large Fungi (as Merulms lacrymans), the water is 

 forced out in drops from the upper part, it having been absorbed by the lower parts 

 which perform the function of roots and press it upwards. 



Fluid however not unfrequently appears in drops in places where there can 

 be no pressure directed upwards from the root. Thus the nectaries of flowers, 

 as those of Fritillaria imperialis, exude drops of nectar even when the stem is 

 cut off from the root and merely placed in water. In this case the forces which 

 cause the pressure must arise in the upper masses of tissue, perhaps even in 

 the flower, for the water is conveyed to the cut stem not by pressure but by 

 suction. 



The phenomenon known as the Bleeding of wood cut in the winter must not 

 be confounded with this. This bleeding occurs when the cut branch or piece of 

 stem, previously cold and saturated with water, is rapidly warmed; the air which 

 is enclosed with the water in the cells and vessels of the wood expands, and forces 

 the water out where it can find an opening. If the piece of wood is again cooled, 

 the air contracts, and the water in contact with the section is again sucked in. It 

 is evident that these expansions and contractions of air in the wood must also take 

 place when the woody substance of the tree is uninjured; and hence currents are set 

 up from the parts which are becoming warmer to those which are becoming cooler, 

 and tensions are brought about. All this however happens only so long as air as 

 well as water is found in the cavities of the wood, as is the case in the winter 

 and spring before the leaves unfold and evaporation begins. 



Although the movements of water in plants have been copiously investigated and 

 discussed for nearly 200 years, it is nevertheless still impossible to give a satisfactory 

 and deductive account of the mode of operation of these movements in detail^ This 

 much appears certain, that the ultimate forces concerned are always capillarity and 

 diffusion (in the broadest sense of the term). But since in the living plant these forces 



globosa, by the moderate pressure of a cohimn of mercury, drops of water at once exude from the 

 large stomata' (Bot. Zeit. 1869, No. 52, p. 882), 



^ [The liquid contained in the pitcher-like organs of Sarracenia, Nepenthes, Cephalotus, 

 &c., is not pure water. Dr. Volcker (Ann. and Mag. of Nat. Hist. Vol. IV, p. 128, and Phil. Mag. 

 Vol. XXXV, p 192) states that it is generally clear and colourless, rarely yellowish, and red- 

 dens litmus. The proportion of residue left on evaporation varies from 0-27 to 0-92 p. c. This 

 residue consists of 38-61 p. c. organic matter, chiefly malic acid with a little citric acid, 50-02 p. c. 

 potassium chloride, 6-36 p. c. soda, 259 p. c. lime, and 2-59 p. c. magnesia. Dr. Buckton (Nature 

 Vol. HI, p. 34) found that the liquid contained in the pitcher-like labellum of Coryanthes consists of 

 98-51 p. c. water and volatile oils, and 1-49 P- c non-volatile residue. It is clear and somewhat 

 glutinous in consistence, with a high refractive power, and a sp.gr. 1-062; neutral to test-paper; 

 on evaporation it becomes milky, finally yielding a transparent gum insoluble in alcohol.— Ed.] 



^ Although Dr. Miiller, in the second part of his ' Botanische Untersuchungen (Heidelberg 1872) 

 assumes that he has actually accomplished this, those only will believe this who are entirely 

 ignorant of vegetable physiology. 



