THE RAPIDITY OF GROWTH 17 



millimetre-minute units, whereas in the case of a bacterium which can 

 double its length in twenty minutes the growth-coefficient would not be 

 more than 0-05. This latter is however higher than in most roots, shoots, 

 hairs, and leaves, for it is rarely that a doubling of the length occurs within 

 from one to two hours even in the most rapidly growing zones of these 

 organs, the maximal growth-coefficients therefore lying between 0-016 and 

 0-008. It is mainly the small size of bacteria which renders possible the 

 rapid nutrition necessary for their rapid growth, whereas the growing apex 

 of a fungal hypha is nourished by the somatic regions behind it. 



A hypha of Botrytis rinerea may elongate 1-08 to 2-04 mm. in length in 

 an hour, in spite of the small size of the growing zone (0-018 mm.). This growth- 

 coefficient (i to 2 mm. per mm. per minute) is greater than that of Phy corny ces 

 nitens (0-12 to 0-3), which with a growing zone of 0-2 to 0-5 mm. (Errera, 1. c. 

 p. 535) elongates 3-6 mm. during the 60 minutes when growth is at its maximum. 

 According to Pfitzer 1 , the hypha of Ancylistes dosterii may elongate as much as 

 01 mm. per minute, but since the length of the growing region is unknown, the 

 growth-coefficient cannot be determined. The latter is probably even higher in 

 the stalk of Coprinus stercorarius , which according to Brefeld 2 may increase in 

 length 13-5 mm. in one hour (0-225 mm. per minute), while in Dictiophora 

 phalloidea, one of the larger Phalloideae, A. Moller 3 has observed an elongation 

 of 120 mm. in two hours, or i mm. per minute. A good instance of rapid 

 growth in length is afforded by Oedogonium when the ring of deposited cellulose 

 stretches to the full possible extent. 



The apically growing pollen-tubes of flowering plants seem in a few cases 

 to attain a rapidity of growth equal to that exhibited by Botrytis*. Very rapid 

 elongation also occurs during the stretching-growth of the staminal filaments of 

 Triticum and Secale^ for these, according to Askenasy, may increase in length from 

 4 to 7 mm. in two minutes, that is, by 37-5 per cent, per minute 5 (linear growth- 

 coefficient = 0-375). The most rapidly growing zone in the root of Vicia (Figs, i 

 and 2) elongates from i mm. to 2-3 mm. in six hours, which gives a rapidity of 

 growth of 0-36 per cent, per minute. A bamboo shoot which grows 913 mm. longer 

 in twenty-four hours (0-635 mm. per minute) and which has a growing zone 50 mm. 

 in length (G. Kraus, 1. c.) has a growth-coefficient of 0-0127 (1-27 per cent, per 

 minute). As a further instance of rapid growth the leaves of Victoria regia may 

 be mentioned, which according to Caspary may become 308-3 mm. longer and 

 367 mm. broader in twenty-four hours 6 . 



1 Pfitzer, Monatsb. der Berl. Akad., 1872, p. 384; Beobachtungen ii. Bau u. Entwickelung der 

 Orchideen, 1882, p. 2 (Verb. d. natnrh.-med. Vereins zu Heidelberg). 



2 Brefeld, Unters. ii. Schimmelpilze, 1877, Heft 3, p. 61. 



3 A. Moller, Schimper's Mittheil. a. d. Tropen, 1895, Heft 7, p. 119. 



4 Lidforss, Jahrb. f. wiss. Bot., 1899, Bd. xxxni, p. 301. Cf. also Stammeroff, Flora, 1897, p. 147. 

 On the slower growth of hairs see Reinhardt, 1. c., p. 522. 



5 Askenasy, Verhandl. d. naturh.-med. Vereins zu Heidelberg, 1879, N. F., ii, p. 246 ; V. Rimpau, 

 Bot. Centralbl., 1883, Bd. xn, p. 6. 



6 Caspary, Flora, 1856, p. 136 ; O. Drude, Nov. Act. d. Leop.- Carolin. Akad., 1881, Bd. XLiil, 



PFEFFER. II 



