MOVEMENT OF WATER IN PLANTS, 6y'J 



Striking in the Maize), Aroideae, Alchemilla^^ &c., when transpiration is diminished 

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

 increased by warm damp earth. Even in unicellular plants, or those which 

 consist only of rows of cells, as the Mucorini (e. g. Pilobolus crystallinus), Pem'cillium 

 glaucum, and the large Fungi (as Merulius 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 

 b'e no pressure directed upwards from the root. Thus the nectaries of flowers, 

 as those of Fritillaria imperialism and the glands in the pitchers of Nepenlhes ^, &c., 

 exude drops of liquid 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 organ itself, 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 transpiration 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 



^ According to Duchartre, De la Rue, and Rosanoff, the exudation usually takes place through 

 stomata, which are either developed in a peculiar manner, or are very large (water-pores), or 

 possess the ordinary form. De Bary remarks in connection with this : — ' If water is forced 

 into the wood of a branch of a plant adapted to the purpose, e. g. Fuchsia globosa, by the moderate 

 pressure of a column of mercury, drops of water at once exude from the large stomata ' (Bot. Zeitg. 

 1869, No. 52, p, 882). [This subject has been further investigated by Moll (Med. d. k. Akad. v. 

 Wet. XV. 2, 1880 : see also Nature, vol. XXII, 1880.] 



^ [The liquid contained in the pitcher-like organs of Sarracenia, Nepenthes, Cephalolus, &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 reddens 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, 5002 p. c. potassium 

 chloride, 6*36 p. c. soda, 2*59 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*5 1 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. See 

 paragraph {e) in the appendix to this section.] 



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

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

 of vegetable physiology. 



