150 THE MECHANISM OF ABSORPTION AND TRANSLOCAT1ON 



absorption of water and salts. The subterranean absorptive and anchoring 

 root-systems of both the higher and lower plants develop according to these 

 principles, and indeed the same laws govern the development of the absorp- 

 tive organs of fungi, organisms which can only absorb their nutriment from 

 organic substances. The many and varied specific peculiarities presented 

 by different root-systems cannot be discussed or even indicated here, but 

 instead it mu.st suffice to give an account of the typical root-system of 

 one of the higher plants. 



The formation of lateral roots commences shortly after the radicle 

 penetrates the soil l . These increase in length so as to cover a large area, 

 while by means of tertiary branches of limited growth, which grow out in 

 all directions, a very thorough absorption of moisture becomes possible 2 . 

 Root-hairs arise from the young roots of most terrestrial plants, and burrow 

 between the particles of earth, so that in this way the extent of absorptive 

 surface may be markedly increased, often as much as from five to twelve 

 times 3 . These root-hairs come into very close connexion with the earthy 

 particles, which often become partially imbedded in their walls, and may cause 

 the root-hairs to assume very peculiar shapes. Frequently, it is impossible 

 to remove all of the particles without injuring the root-hair 4 (Fig. n). 



The parts of the root are only of importance for absorption during 

 a limited period, for as the well-known change of colour indicates, when the 

 root grows older and deep- seated cork 5 is formed, the cortex, epidermis and 

 root-hairs die and peel off, while at the same time the absorptive power 

 almost entirely disappears. Since, moreover, the smaller absorptive roots 

 usually die after having persisted for a certain length of time, it is only 

 by continued growth and by the formation of new roots that an adequate 

 functional activity of the root-system is maintained, so that as the area of 

 ground covered becomes larger, the extent of absorptive surface also increases. 

 It is owing to this close union between the root-hairs and the soil particles 

 that when roots are carefully lifted from the soil, the latter remains attached 

 wherever root-hairs are present 6 . Thus in the seedling of Sinapis shown 



1 The absorption of water by seeds, and their swelling, cannot be entered into. The seed-coats 

 in many cases only allow water to penetrate with difficulty, so that when incisions are made in them, 

 the seeds swell much more rapidly. In other cases, water penetrates mainly or more rapidly at 

 certain points. See Detmer, Physiologic des Keimungsprocesses, 1880, and the literature quoted in 

 Sect. 12. On the existence of special regions for the absorption of water, see Mattirolo and 

 Buscaloni, Bot Zeitg., 1890, p. 397; Haberlandt, Physiol. Anat, 1884, p. 313. On the way in 

 which germinating seedlings become attached, see Klebs, Unters. a. d. Bot. Inst. z. Tubingen, 1885, 

 J > P- 537. &c. 



a Th. Hartig, Anat. u. Physiol. d. Holzpflanzen, 1878, p. 251 ; Resa, Uber die Periode der 

 Wurzelbildung, Bonner Dissertation, 1877; Frank, Lehrb., 1892, Bd. I, p. 316. 



3 Fr. Schwarz, Unters. a. d. Bot. Inst. z. Tubingen, 1883, Bd. I, p. 140. 



* See F. Schwarz, 1. c., pp. 142, 179. 



5 Hoveler, Bot. Zeitung, 1877, p. 785. 



6 Treviranus, Physiologic, 1838, Bd. n, p. 113. By imbedding in gelatine to which formic 



