THE CARDINAL POINTS FOR GROWTH 



the discordant results of different authors are partly the result of the different 

 methods employed. Thus in some cases the temperatures observed were those 

 at which germination commenced (Sachs), and in others they were those at which 

 pre- existent growth ceased (de Vries, Kirchner, 

 &c.). When all the different phases of growth 

 are to be investigated, the best results will be 

 obtained with rapidly developing organisms. In 

 many cases, however, sufficient precautions have 

 not been taken to maintain constant temperatures. 

 These can easily be assured in the hot chambers 

 used for the culture of bacteria *. In the case 

 of plants requiring light, it is best to place these 

 in bell-jars sunk under water in a large aqua- 

 rium kept at constant temperature. A steady 

 stream of dry air must be drawn through the 

 bell-jar, and must be warmed to the same tem- 

 perature by passing it through a coiled tube 

 immersed in the water of the aquarium 2 . A sim- 

 pler arrangement (Fig. 17) suffices to keep the 

 temperature constant to iC. in diffuse day- 

 light. 



To obtain low temperatures, cellars, ice- 

 chests, water cooled by ice, &c., may be used 3 , 

 but no good automatic arrangement has as yet 

 been devised 4 . Many hot stages and chambers 

 of greater or less accuracy have been constructed 

 for microscopical observations 5 . In Pfeffer's hot 

 stage, the hot chamber is surrounded by water at 

 constant temperature, and considerable accuracy 

 is ensured 6 . 



FIG. 17. Apparatus for constant tempera- 

 ture. Between the double walls of the 

 zinc vessel z is water kept at constant 

 temperature by the regulator r t and j 

 are thermometers. 



The following is the chief literature concerned with the determination 

 of the cardinal points of the higher plants : 



Sachs, 1860, I.e.; Koppen, Warme u. Pflanzenwachsthum, 1870; de Vries, 

 Materiaux p. 1. connaissance de 1'influence d. 1. temperature, 1870 (repr. from 



1 Figures are given in most price-lists. Cf. also Pfeffer, Zeitschr. f. wiss. Mikr., 1890, 

 Ed. vn, p. 443, and in Ber. d. Bot. Ges., 1895, p. 49, Pfeffer describes the arrangement for a warm 

 room at constant temperatures. 



2 An arrangement suitable for special purposes was used by Jost, Bot. Ztg., 1897, p. 25. 



3 Uloth (Flora, 1871, p. 185; 1875, p. 266) observed that the radicles of certain plants grew 

 on ice, and were able to penetrate it owing to the * plasticity ' of the ice under the pressures exerted 

 by the root-apex. 



4 Cf. Oltmanns, Jahrb. f. wiss. Bot., 1892, Bd. XXIII, p. 362. 



5 See Zimmermann, Das Mikroskop, 1895, p. 224; Behrens, Zeitschr. f. wiss. Mikr., 1895, 

 Bd. xii, p. 2 ; R. Kraus, Centralbl. f. Bact., 1898, I. Abth., Bd. xxin, p. 16. 



6 Pfeffer, Zeitschr. f. wiss. Mikr., 1890, Bd. vn, p. 433. A slightly improved form is 

 figured by Ewart, Protoplasmic Streaming, Clar. Pres^, 1903, p. 60, Fig. 9. 



G 2 



