THE CARDINAL POINTS FOR GROWTH 81 



The same applies to Bacillus a/ithracis, B. tumescens, and B. subtilis^. 

 Similarly, many of the higher plants are unable to flower at low temperatures at 

 which vegetative growth continues, or at high ones which cause it to increase in 

 activity 2 . 



In some cases germination may be possible at temperatures which do not 

 permit further growth 3 , whereas in other cases the stimulus of a high (or low) 

 temperature may be necessary to start the germination of plants which are 

 subsequently able to develop at a more equable one. This may apply to 

 Piiolohis torridus, whose spores only germinate at from 30 to 35 C.* More- 

 over, the germination of certain seeds, such as cucumbers, is accelerated by 

 previous warming. 



Formative changes. These are very pronounced when we are dealing with 

 the formation or suppression of perennating parts or reproductive organs. Apart 

 from this, the general shape of the plant may be influenced by the temperature, 

 though usually not to any great extent. Thus, green plants grown at low 

 temperatures are usually more compact 5 , and in the case of fungi and bacteria 

 peculiar growth-forms may be produced at abnormal temperatures 6 . 



A change of temperature is usually rapidly followed by a corresponding 

 alteration in the activity of growth 7 . A certain transient disturbing 

 influence is probably also exercised, although this is usually not sufficiently 

 pronounced to perceptibly affect growth. In the case of the thermonastic 

 movements of leaves and flowers, a change of temperature produces 

 a transient acceleration of growth 8 . Again, a change from a low to a more 



208. On the conditions for spore-formation cf. Beyerinck, Centralbl. f. Bact. u. Parasit, 1898, 2. Abth., 

 Ed. IV, p. 662. 



1 O. Schreiber, Centralbl. f. Bact., 1896, Bd. XX, p. 431. There, and also by Fliigge, Mikro- 

 organismen, 1896, 3. AnfL, Bd. I, p. 432, additional literature is quoted. 



2 Mobius, Beitr. z. Lehre v. d. Fortpflanzung d. Gewachse, 1897, p. 108, and the literature there 

 given; Schimper, Pflanzengeographie, 1898, p. 51. 



3 Sachs, jahrb. f. wiss. Bot, 1860, Bd. n, p. 336 (seeds) ; Wiesner, Sitzungsb. d. Wiener Akad., 

 1873, Bd. LXVII, i. Abth., p. 9 (Penicilliuni). 



* Brefeld, Bot. Unters. ii. Schimmelpilze, iSSi, Heft 4, pp. 20, 71. 



5 Kerner, Pflanzenleben, 1887, Bd. I, p. 408; Bd. II, p. 497; Schimper, Pflanzengeographie, 

 1898, p. 40. On seedlings cf. Sachs, Jahresb. d. Agriculturchem., 1859-60, p. 98; Bialoblocki, 

 Versuchsstat., 1870, Bd. xm, p. 441. On the length of the growing zone in roots cf. Popovici, Bot. 

 Centralbl., 1900, Bd. LXXXI, p. 91. On the influence of the temperature on the seasonal variations 

 of butterflies cf. O. Hertwig, Zellen u. Gewebe, 1898, p. 120; Standfuss, Biol. Centralbl., 1899, 



. Bd. xix, p. 75. 



6 On acetic bacteria cf. Hansen, Meddelelser fra Carlsberg Laboratoriet, 1894, Bd. ill, 

 Ref., p. 198; Lafar, Techn. Mykologie, 1897, Bd. I, p. 347. [Vochting (Bot. Ztg., 1902, p. 88) 

 finds that ' Marjolin ' potatoes form vegetative shoots only above 20 C., while at very low 

 temperatures, and also when the supply of water is deficient, they produce tubers only.] 



7 Pedersen, Arb. d. Bot. Inst. z. Wiirzburg, 1874, Bd. I, p. 563 ; Askenasy, Ber. d. Bot. Ges., 

 1890, p. 75; Godlewski, Anzeig. d. Akad. d. Wiss. in Krakau, 1890, p. 171; True, Annals of 

 Botany, 1895, Vol. ix, p. 390. Koppen (Warme und Pflanzenwachsthum, 1870; Bot Jahresb., 

 1875, p. 778) incorrectly supposed that a transitory retardation of growth ensued. 



3 The stimulating effect of a rise of temperature may differ from that produced by a corre- 

 sponding fall. According to Kinzel (Versuchsstat., 1900, Bd. LIV, p. 134) the germination of 

 various seeds is favoured by changes of temperature. 



PFEFFER. II G 



