16 GROWTH 



individuals 1 . In the case of a cylindrical form, of length 0-002 and diameter 

 o-oo i mm., 636 millions would have a total volume of i cubic mm. Hence 

 the growth after one day would correspond to a volume of 0-022 cubic mm., after 

 two days to 442 cm., and after three days to 7^ million litres, or more than 7 J mil- 

 lion kilogrammes. A few days later the mass of bacteria would surpass the volume 

 of the earth. The 16^ million individuals resulting at the end of the first day would 

 form, when placed end to end, a thread 33 metres long, and this would become 

 563,000 kilometres long at the end of the second day (281^ billion individuals), 

 or about 14 times longer than the circumference of the earth at the equator. 



The harvest yielded by a hectare (2^ acres) in the course of a year is trifling 

 as compared with these practically unattainable values, for it amounts to about 

 8,000 kilogrammes dry weight (40,000 when moist) in the case of ordinary crops, while 

 actively growing forest trees of from 40 to 120 years of age produce per hectare 

 from 2,000 to 4,000 kilogrammes dry weight of wood, to which the weight of the 

 fallen foliage must be added 2 . In favourable tropical climates these values may be 

 doubled or trebled 3 . Reorders in fact observed that in Java the rapidly growing 

 Albicda moluccana became 3 metres high in eight months 4 , whereas Larix europaea 

 increases by about 0-25 metres, and Pinus sylvestris by 0-12 metres in the same 

 time in Northern Europe. In nine years Albicda becomes 33 metres high in Java, 

 whereas the conifers mentioned, and also the beech, require 120 to 160 years to 

 attain this height 5 . 



The amount of growth is dependent upon the size of the growing 

 region, and upon the duration and activity of growth in it. The relative 

 rapidity of growth 6 in a growing zone is given by noting the increment of 

 growth of a unit length (linear growth-coefficient), area (superficial growth- 

 coefficient), or volume (cubical growth-coefficient) in. unit time. The actual 

 rapidity of growth is not very great in such plants as Bambusa and Humulus, 

 for the rapid elongation of these plants is mainly due to the abnormal length 

 of the growing zones. On the other hand the linear growth-coefficient is very 

 high in many fungi, in which the growing zone is restricted to the extreme 

 apex of the hypha. This growing zone, which is not longer than 0-018 mm. in 

 Botrytis cinerea, may increase in length by 0-018 to 0-034 mm. per minute, 

 i.e. by 100 to 200 per cent. 7 This equals a growth-coefficient of i to 2 in 



1 Cf. Cohn, Die Pflanze, 1882, p. 438. 



2 Cf. Schwarz, Forstliche Bot., 1892, p. 160, and similar sources. 



3 See also Giltay, Bot. Centralbl., 1898, Bd. xvin, p. 694. 



* Koorders, Beibl. z. Bot. Centralbl., 1895, Bd. v, p. 318. [Certain herbaceous temperate plants 

 may grow even more actively, viz. Helianthus annuus and Heracleum giganteum may become a to 4 

 metres high in from four to six months.] 



5 Cf. Ebermayer, Physiol. Chem., 1882, p. 41 ; also Hartig, Lehrb. d. Anat. u. Physiol., 1891, 

 p. 257 seq. 



6 Sachs, Lehrbuch, 1873, 3. Aufl., p. 731. Sachs' use of the term 'energy of growth' is not to 

 be recommended, since this term should be employed in its strict physical sense. Cf. Pfeffer, 

 Euergetik, 1892, p. 231. Similarly the term ' rapidity of growth ' is preferable to Askenasy's ' intensity 

 of growth' (Verhandl. d. naturhist.-med. Vereins z. Heidelberg, 1878, Bd. II, p. 10). 



7 Reinhardt, Jahrb. f. \viss. Bot., 1892, Bd. xxm, p. 490. 



