THE RAPIDITY OF GROWTH 15 



It is evident therefore that the contraction is not the result of a fall of osmotic 

 pressure in the active cells, and it is also clear that the shortening of the root 

 is not necessarily connected with the commencement of secondary growth. Several 

 problems still remain to be solved, as for example whether any changes occur in 

 the elasticity of the walls of the active cells, and whether their power of stretching 

 undergoes local modification. 



SECTION 5. The Rapidity of Growth. 



Under optimal conditions the activity of growth may be accelerated to 

 a certain specific limit dependent upon the character and age of the plant 

 examined. In a condition of nature the average growth is slower than this, 

 although the maximal possible activity for a particular plant may 

 occasionally be more or less closely attained for short periods of time. 

 The stems of climbing plants, such as Humulus and Cucurbito> may become 

 12 metres long in the course of a single summer, whereas those of seedlings 

 of Quercus and Abies become barely 12 centimetres long in the same time, 

 and many lichens grow not more than 2 to 5 millimetres in the course of a 

 year even under favourable conditions 1 . On the other hand a bamboo 

 shoot has been observed to grow from 50 to 75 centimetres in length in 

 twenty-four hours 2 , and Bambusa gigantea may become 8-75 metres high 

 in thirty-one days 3 . All tropical plants do not however grow with special 

 rapidity, but in a warm moist climate, and in the absence of a winter- 

 resting period, a greater total growth is possible, even in plants which do 

 not grow more rapidly than those of temperate regions. 



Even more active powers of growth are possessed by the cosmopolitan 

 bacteria and fungi. In bacteria especially, since every cell remains 

 embryonic, the total growing mass rapidly increases if the supply of food 

 is ample and the injurious metabolic products are continually removed. On 

 the other hand the growing zones in Somatophytes increase but slowly, 

 or under special conditions not at all. 



A rapidly growing bacterium can produce under favourable conditions two 

 individuals of similar size within 20-30 minutes *. Even at the rate of one division 

 an hour, the progeny of a single bacterium would amount in twenty-four hours to 

 i6J millions, in two days to 281^ billions, and in three days to 4,772 trillions of 



1 Krabbe, Cladoniaceen, 1891, p. 131. Cf. also Vallot, Rev. gen. de Bot., 1896, T. vnr, p. 201 ; 

 C. F. W. Meyer, Nebenstud. meiner Beschaft. im Geb. d. Pflanzenkunde, 1825, p. 39 ; G. Bitter, Jahrb. 

 f. wiss. Bot., 1898, Bd. xxxii, p. 126. For instances of more rapidly growing lichens see Funfstiick, 

 Beitr. z. wiss. Bot., 1895, Bd. I, p. 216. 



2 Kraus (Ann. du Jard. Bot. de Buitenzorg, 1895, T. xn, p. 199) observed 57 cm. growth 

 in twenty-four hours in a species of Dendroealamus, and in Kew Gardens a growth of 91 cm. has 

 been seen in the same time (cf. Kraus, 1. c., p. 198). See also Dingier, Flora, 1897, Erg.-bd., 

 p. 281 ; Schibata, Jour, of the College of Science, Tokio Univ., 1900, Vol. xin, p. 456. 



3 According to Wallich. Cf. G. Kraus, 1. c., p. 197. 



* Buchner and Nageli, Sitzungsb. der Miinchener Akad., 1880, p. 375 ; Brefeld, Unters. iiber 

 Schimmelpilze, 1881, Heft 4, p. 46; Koch, Bot. Ztg., i8S8, p. 294; Fliigge, Mikroorganismen, 

 1896, 3. Aufl., Bd. i, p. 420. 



