NOTES 7f,:: 



not the same in the two cases. It is highly probable that all these features are 



correlated with the physical characteristics of the two forma of wood, 



364. Sachs: Textbook of Botany (2nd Engl, ed.), p. 813. DeVries: Flora, 1872, 

 p. 241. Id. Arch. Neerl. 11, 1876. Krabbe : Sitzb. Berlin, 1882, pp. 1093 sqq. 

 Russow : Neue Dorptsche Zeitung, 1881. Wieler : P.J. 18, 1887. Gnentzsch : 

 Flora, 1888. R. Hartig : Unters. a. d. forstbot. Inst. z. Miinchen, 1, 1880. Id. 

 Das Holz. d. Nadelwaldbaume, 1885. Jost : B.Z. 1891. Jahn : Bot. Centr. 59, 

 1894. Lutz : Ber. 13, 1895. Cf. also Funfstuck's Beitr. 1. 



365. G. Haberlandt : Phys. Pflanzenanat, 1st ed. 1884, p. 371. Id. Ber. 1895. 

 Strasburger : I.e. [355], pp. 945 sqq. R. Hartig : Allg. Forst- u. Jagdzeitung, 1889. 

 Id. Forstl. naturw. Zeitschr. 3, 1894. F. Schwarz : Physiologische Unters. iib. 

 Dickenwaehstum u. Holzquahtat v. Pinus sylvestris, Berlin, 1899. Ursprung : 

 Beitr. z. Anat. u. Jahresringbildung tropischer Holzarten (Inaug.-Diss.), Basle, 

 1900. Metzger : Naturw. Zeitschr. f. Forst- u. Landw. 1908. 



Metzger, who is evidently unacquainted with the author's ecological explanation 

 of the formation of annual rings, attempts to refer the structural differences between 

 spring- and autumn- wood entirely to mechanical causes. " With a given expendi- 

 ture of material, the maximum of inflexibility can only be attained, if the specialised 

 mechanical cells are massed near the periphery of the annual rings ; the weaker 

 conducting elements thus naturally come to take up their position on the inner 

 side of the rings, anel are consequently produced at the beginning of each vegetative 

 season." According to Metzger, therefore, the conducting tissue appears first, not 

 because it is needed early in the season, but merely because it is necessary that the 

 mechanical tissue should take up a peripheral position. This interpretation might 

 pass muster, if the woody cylinder were composed of a few very wide annual 

 rings. As, however, the converse is actually the case, the annual rings being numerous 

 and comparatively narrow, the location of the mechanical tissue in the individual 

 rings is a matter of very slight importance from the ecological point of view. This 

 conclusion may also be directly arrived at from Metzger's own calculations. He 

 considers the case of a stem 20 cm. in diameter, to which is to be added an annual 

 ring of 3 mm. total diameter, made up of 2 mm. of spring- wood and 1 mm. of autumn- 

 wood. Under certain conditions, the original strength of the stem may be expressed 

 by the figure 4214-61. If a homogeneous ring 3 mm. in width is added, the value rises 

 to 4596-93, an increase of 382-32 units. If the ring consists of 2 mm. spring- wood 

 and 1 mm. autumn- wooel, the new value is 4601-35, an increase of 386-74 units, 

 or only 4-42 units more than in the first case. If the mechanical tissue were formed 

 first and the conducting tissue later, the new value would be 4592-47, an increase 

 of 377-86 units, or 8-88 units less than with the converse arrangement. But it 

 obviously cannot be of much importance whether the strength of a stem is raised 

 from 4214-61 to 4592-47, to 4596-93 or to 4601-35; the differences between the 

 three new values only amount to -1 to -2 per cent., anel are therefore of no ecological 

 importance. Moreover, these differences diminish as the girth of the trunk increases, 

 so that the location of the mechanical tissue in the annual rings becomes less and 

 less important as the tree grows oleler ; nevertheless, the most recently formed annual 

 rings in an aged stem are just as sharply defined as the oldest ones. Metzger's attempt 

 to arrive at a purely mechanical solution of the problem, cannot therefore be regarded 

 as a success. 



366. Kny : Verb. Bot, Ver. Brand. 1879. Wilhelm- : Ber. 1883. 



367. Sanio : P.J. 8, pp. 401 sqq. 



3 B 



