312 METAMORPHOSIS 



MoLiscH. 1897. Unters. iib. das Erfrieren d. Pflanzen. Jena. 



Muller-Thurgau. 1886. Landw. Jahrb. 15, 453. 



Noll. 1888. Arb. bot. Inst. Wiirzburg, 3, 466. 



Noll. 1900. Ber. d. bot. Gesell. 18, 444. 



NoRDHAUSEN. 1903. Ber. d. bot. Gesell. 21, 30. 



Overton. 1899. Jahrb. f. wiss. Bot. 2,2)^ ^7^- 



Palladin. 1890. Ber. d. bot. Gesell. 8, 364. 



Popovici. 1900. Bot. Centrbl. 81, ^Z- 



Prantl. 1873. Arb. bot. Inst. Wurzburg, i, 371. 



Raciborski. 1900. Bull. Inst, de Buitenzorg, No. 6. 



Reinke. 1876. Bot. Ztg. 34, 143. 



Reinke. 1893. Sitzungsber. Berliner Akad. 527. 



Rosenvinge. 1889. Revue gen. de bot. I, 153. 



Sachs. 1862 and 1864. Flora, 45, 186 ; 47, 505. 



Sachs. 1863. Bot. Ztg., Beilage. 



Sachs. 1864. Flora, 47, 8. 



Sachs. 1872. Arb. bot. Instit. Wurzburg, i, 99. 



Sachs. 1887. Ibid. 3, 371. 



Schimper. 1885. Jahrb. f. wiss. Bot. 16, i. 



Stahl. 1883. Jen. Zeitschr. f. Naturwiss. 16. 



Stahl. 1884. Ber. d. bot. Gesell. 2, 389. 



Stahl. 1885. Ibid. 3, 334. 



Stameroff. 1897. Flora, 83, 135. 



Strehl. 1874. Langenwachstum d. Wurzel u. des hypocotylen Gliedes (Diss. 



Leipzig). 

 Thiselton-Dyer. 1899. Proc. Roy. Soc. 65, 362. 

 Vochting. 1878. Organbildung im Pflanzenreich, I. Bonn. 

 VocHTiNG. 1887. Bibliotheca botanica, Heft 4. 

 Vochting. 1894. Jahrb. f. wiss. Bot. 26, 438. 

 Vochting. 1902. Bot. Ztg. 60, 87. 



Wiesner. 1873. Sitzungsber. Wien. Akad. Math.-nat. Kl. 67, i, 9. 

 WiESNER. 1 89 1. Ber. d. bot. Gesell. 9, 46. 



Wiesner. 1894. Sitzungsber. Wien. Akad., Math.-nat. Kl. 103, 401. 

 Wiesner. 1893, 1895, 1900. Photometr. Untersuch. auf pflanzenphys. Gebiete. 



Sitzungsber. Wien Akad. Math.-nat. Kl. 102 (1893), 104 (1895), I09 (1900). 

 Wiesner. 1902. Biologie d. Pflanzen. Vienna. 

 [Wiesner. 1904. Sitzungsber. Wiener Akad. 113, T. 469.] 

 [Wiesner. 1905. Ibid. 114, T. 77.] 

 Winkler. 1900, a. Jahrb. f. wiss. Bot. 35, 449. 

 Winkler. 1900, b. Ber. d. bot. Gesell. 18, 297. 



LECTURE XXV 



EXTERNAL CAUSES OF GROWTH AND FORMATION. II 



In addition to heat and light, gravity must be considered as a factor fre- 

 quently influencing the growth and shape of plants. To begin with it may be well 

 to illustrate by means of a few examples that the weight of the entire plant or of 

 its parts is not only not injurious, but is even helpful to vitality. Great weight, 

 absolute or relative, is naturally, for purely mechanical reasons, a disadvantage 

 in the distribution of seeds, and hence we find developed in many cases floats, 

 wings, or other adaptations of the most varied character. In aquatic plants 

 also we find the vegetative organs provided with aids to flotation, for the water 

 has to support the weight of the organs which terrestrial plants themselves 

 support. Land plants possess, indeed, special mechanical tissues which are 

 absent from aquatics. Twining and climbing plants exhibit special adaptations 

 (Lectures XXXV and XXXVIII), e. g. holdfasts of various kinds which render 

 the development of a special strengthening skeleton more or less unnecessary. 



All these adaptations are special peculiarities of the plant as such, which 

 are in no respect due to the direct influence of gravity on the individual. 



