73 INFLUENCE OF THE EXTERNAL CONDITIONS ON GROWTH 



just as the spores of certain bacteria do when boiled. Hence all such observations, 

 and more especially those dealing with transitory temperatures, need to be accepted 

 with great caution. How easily errors may arise is shown by the fact that Hoppe- 

 Seyler observed a surface-temperature of 44-45 C. in a streamlet whose deeper 

 layers were cooled by the continual access of cold water to 25 C., and contained 

 numerous fishes that fell into heat-rigor when brought to the surface. Observations 

 with regard to temporary low temperatures are equally liable to error l . 



No plant is known which can accommodate itself to the lowest as 

 well as to the highest extremes given above, the greatest observed range 

 amounting to less than 50 C., and being usually much less than this, as 

 is in fact of necessity the case when the maximal limit is low. The latter 

 applies to Hydrurus, whose maximal limit of 16 C. is 60 C. lower than that 

 of thermophile bacteria. Thermophile organisms have a high optimum as 

 well as a high maximum, but a moderate rise of the minimum point does 

 not always involve a corresponding rise of the optimum. 



Owing to the dissimilarity between the situations of their cardinal 

 points, certain plants grow best at temperatures which do not permit of the 

 growth of others. Thus, a few species of thermophile bacteria first begin 

 to develop at temperatures sufficiently high to kill most plants, and their 

 most active growth occurs in nutrient solutions hot enough (60-70 C.) to 

 scald one's finger. The spores of these organisms are widely distributed, 

 but it is only rarely that they find the temperatures necessary for their 

 development. Such organisms as these, as well as the thermophile 

 Aspergillus fumigatus, are of importance in that they can continue the 

 process of decomposition in manure-heaps and the like, in which the 

 fermentative activity of the commoner micro-organisms has caused so great 

 a rise of temperature as to prevent their further development. 



The greatest extremes are shown among fungi, bacteria, and the lower 

 algae, although most of these plants exhibit a range of accommodation 

 little or no greater than that of flowering plants, in which the optimum lies 

 usually between 24 and 34 C., the maximum between 26 and 46 C., and 

 the minimum between o and 16 C. The minimum is often higher in tropical 

 plants than in those of temperate regions 2 , although here also plants exist 

 which have a high minimum. Other plants, such as Hydrurus and Ulothrix 

 zonata, require a low temperature, so that it is only in spring that most 

 streams are cold enough for them, and in summer they die down and 

 perennate by means of resting spores 3 . 



1 Cf. Ewart, Annals of Botany, Vol. xn, 1898, pp. 367-73. 



3 This was first pointed out by de Candolle, Physiologic, 1833, Bd. II, p. 277. See also Sachs, 

 Jahrb. f. wiss. Bot., 1860, Bd. H, p. 365 ; Haberlandt, Wiss. Unters. a. d. Geb. d. Pflanzenbaues, 

 1875,1, p. 117. 



3 Cf. the literature quoted, and also G. Lagerheim, Ber. d. Bot. Ges., 1888, p. 73 ; Oltmanns, 

 Jahrb. f. wiss. Bot., 1891, Bd. XXIII, p. 358; Noll, Flora, 1892, p. 288; Goebel, Pflanzenbiol. 

 Schilderungen, 1893, II, p. 246; Kerner, Bot. Ztg., 1873, p. 437. 



