158 THE MECHANISM OF ABSORPTION AND TRANSLOCATION 



probably be possible in all cases, for then the injurious effects of a sudden 

 change might be avoided. 



SKCTION 27. Absorption of Fluids and Solids by the Sub-aerial Organs. 



The sub-aerial organs of land-plants are specially concerned with gaseous 

 exchange, and under normal conditions have little or nothing to do with 

 the absorption of water as rain or dew, the latter being in general only 

 of importance to the plant as the sources from which the moisture of 

 the soil is derived. As a matter of fact various means are provided for 

 carrying away rain as quickly as possible from the leaves, such as their 

 form, position, movements, and other properties \ while so long as the surface 

 of the leaf is not wetted, no absorption of water is possible. On the leaves 

 of Nelumbium, Nymphaea^ &c., drops of water roll about like globules of 

 mercury on a glass plate without wetting or adhering to any part. This 

 power of remaining umvetted is probably for the purpose of maintaining 

 an unimpaired rate of gaseous exchange, and a fall of rain does not as 

 a general rule block up the stomata, nor does any water pass through 

 them even when completely immersed. 



The function of the cuticularized epidermis of aerial parts is to 

 check transpiration, and hence it can hardly have any marked powers 

 of absorption. If therefore the sub-aerial parts readily absorb water, 

 the plant must either be able to withstand temporary desiccation, or must 

 possess arrangements by which in periods of drought the excessive loss 

 of water can by other means be guarded against, or it must grow in a very 

 moist habitat. All these conditions are found in nature. Among our own 

 plants many mosses and lichens are known which can dry up without 

 being injured, and which, when moistened with water in the form of rain 

 or dew, become at once turgid again and resume the vital activity which 

 was interrupted by desiccation 2 . These mosses and lichens which grow upon 

 bare rocks must indeed obtain all their water in the form of rain and dew, 



earth-roots, cf. Perseke (Formanderungen der Wurzeln in Erde u. in \Yasser, 1877, p. 45). Root- 

 hairs may assume abnormal shapes when suddenly transferred to a new medium. See F. Schwarz, 

 Unters. a. d. Bot. Inst. z. Tubingen, 1883, Bd. I, p. 182; Wortmann, Bot. Zeitung, 1889, p. 279; 

 \Vieler, ibid., p. 550. 



1 Cf. 38, 39; Stahl, Regenfall und Blattgestalt, 1893. 



2 Schioder, Unters. a. d. Bot. Inst. z. Tubingen, Bd. ir, Heft i, 1886. On the special adaptations 

 for the storage of water found in many Musci, cf. Goebel, Pflanzenbiol. Schilderungen, 1889, p. 27 ; 

 Flora, 1893, p. 423 ; Keeble, Annals of Botany, 1895, Bd. IX, p. 59; Jungner, Bot. Centralbl, 1895, 

 Bd. LXI, p. 434. On Hymenophyllaceae, Giesenhagen, Flora, 1890, p. 455. [The dried living 

 cells of such plants contain not air but a more or less perfect vacuum. Hence when moistened 

 they become almost immediately filled with water and turgid, which would otherwise be impossible. 

 (Cf. Kamerling, Hot. Centralbl., Bd. i.xxir, 1897, p. 49.) Plants of Dicramtm scoparium and 

 Cladonia rangiferina, after being kept air-dry for three months, showed an immediate resumption 

 of respiration when moistened, and a power of CO 2 -assimilation at once or after a short latent 

 period: F.wart, Trans. Liverpool Biol. Soc., vol. xi, 1897, p. 152.] 



