340 METAMORPHOSIS 



HANSEN. 1881. Abhdl. d. Senkenbergschen Gesell. 12. 

 HERING. 1896. Jahrb. f. wiss. Botanik, 29, 132. 

 HILDEBRAND. 1898. Die Gattung Cyclamen. Jena. 

 HOFMEISTER. 1 868. Allg. Morphologic. Leipzig. 



OST. 1891. Bot. Ztg. 49, 485. 



osx. 1893. Ibid. 51, 89. 



OST. 1895. Jahrb. f. wiss. Botanik, 27, 403. 

 _OST. 1899-1902. Bot. Ztg. 57, 193 ; 60, 21 ; 60, II, 225. 

 KLEBS. 1903. Willkurliche Entwicklungsanderungen bei Pflanzen. Jena. 

 LEISERING. 1902, a. Flora, 90, 378. 

 LEISERING. i9O2,b. Jahrb. f. wiss. Bot. 37, 421. 

 LEISERING. 1902,0. Ber. d. bot. Gesell. 20, 613. 

 LINDEMUTH. 1901. Ber. d. bot. Gesell. 19, 515. 

 [MASSART. 1898. Memoires Acad. Bruxelles, 57.] 

 [MACCALLUM. 1905. Bot. Gaz. 40, 97 and 241.] 

 [MiEHE. 1905. Ber. d. bot. Gesell. 23, 257.] 

 [MoNTEMARTiNi. 1904. Atti 1st. bot. Pavia, N.S. 10.] 



PETERS. 1897. B. z. K. d. Wundheilung bei Helianthus. Diss. Gottingen. 

 SCHUMANN. 1899. Morphologische Studien. p. 238. Leipzig. 

 SCHWENDENER. 1878. Mechan. Theorie d. Blattstellungen. 

 SCHWENDENER. 1883, &c. Sitzungsbeiichte d. Berliner Akad. 1883, 1895, 



1900, 1901, and Ber. d. bot. Gesell. 20, 249. 

 [SiMON. 1904. Jahrb. f. wiss. Bot. 40, 103.] 

 STRASBURGER. 1901. Jahrb. f. wiss. Bot. 36, 493. 

 VOCHTING. 1878. Organbildung. Bonn. 

 VOCHTING. 1885. Jahrb. f. wiss. Bot. 16, 367. 

 VOCHTING. 1887. Bibl. bot. Heft 4. 

 VOCHTING. 1891. Bot. Ztg. 49, 113. 



VOCHTING. 1892. Ueb. Transplanation am Pflanzenkorper. Tubingen. 

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

 VOCHTING. 1899. Ibid. 34, i. 

 VOCHTING. 1902. Ibid. 38, 83. 

 DE VRIES. 1891. Jahrb. f. wiss. Bot. 22, 35. 

 WIESNER. 1889. Bot. Ztg. 47, i. 

 WINKLER. 1901. Jahrb. f. wiss. Bot. 36, i. 

 WINKLER. 1902. Ber. d. bot. Gesell. 20, 81. 

 WINKLER. 1903. Jahrb. f. wiss. Bot. 38, 501. 



LECTURE XXVII 



PERIODICITY IN DEVELOPMENT. I 



THE developmental processes in organisms are not always carried out with 

 the same degree of activity nor yet at an equal rate. If a plant consists of a 

 single spherical cell this cell can increase only to a certain specific size ; uniform 

 and continuous surface growth with retention of the spherical form is quite im- 

 possible. In the simplest organisms growth after a certain point is followed by 

 cell division, resulting in the formation of two organisms, each of which proceeds 

 to develop in the same way as did the parent. Growth and division follow each 

 other with regular periodicity. Even plants, which as a rule show no cell 

 division (e. g. the Siphonaceae), do not grow uniformly in one direction, but from 

 time to time form lateral branches. The more complicated the organism is the 

 more pronounced do periodic variations in its developmental activity become, 

 due sometimes to more or less recognizable external factors, sometimes to purely 

 internal conditions. One of the most remarkable of these periodicities is the 

 death after a time in many plants of part of the organism, while usually a frag- 

 ment only remains alive and undergoes further development. Not less note- 

 worthy is the phenomenon of hibernation, where all development ceases often 



