RATE OF GROWTH IN RAIN-FOREST PLANTS. 



Our knowledge of the rate of growth of tropical plants is nearly 

 confined to the results of measurements which have been made on 

 leaves and stems of lowland plants in which the rates are conspicuously 

 high. Lock^ found a rate of elongation of 231 mm. per day in the 

 shoots of the giant bamboo, Dendrocalamus, in Ceylon, and MaxwelP 

 observed a rate of 107 mm. per day in the growth of banana leaves. 

 Schimper^ measured the leaves of Amherstia and some other tropical 

 lowland trees and found their rates of growth to be exceedingly rapid. 

 Such high rates of growth have been tacitly credited to all tropical 

 plants, although there are doubtless very many lowland forms in which 

 the usual rates of growth are relatively slow, while slower rates are 

 naturally to be expected in montane tropical regions. 



Only a few weeks of observation in the Cinchona region were nec- 

 essary to convince me that the rates of growth in the native rain- 

 forest vegetation are relatively slow, and that the physical conditions 

 under which they exist are not such as would be conducive to rapid 

 rates. I became interested therefore in the growth behavior of the 

 vegetation, as a summation of the many and less easily measured 

 fundamental activities of the plants, and made both observations and 

 measurements with a view to increasing our knowledge of plant activity 

 in a region which presents equable conditions of temperature and 

 almost uniformly favorable conditions of moisture. 



Attention has already been called to some of the seasonal differences 

 in growth activity which exist between the various species of the 

 rain-forest. It is natural to anticipate differences of rate between 

 plants in which growth is continuous and those in which it is taking 

 place during only a few months or weeks of the year; and there are a 

 few cases in which such differences exist. The growth of Gilibertia 

 and Turpinia is confined to a few weeks in the late spring, and is one of 

 the most rapid growth phenomena in the rain forest. In Cyathea 

 puhescens and other tree ferns the formation of new leaves takes place 

 during the winter and spring, and their elongation is the most rapid 

 growth phenomenon that has come under my notice. The elongation 

 of leaves in all terrestrial ferns is much more rapid than the rate of 

 growth in the leaves of other herbaceous plants, and this is due to 

 the seasonal character of the growth of fern leaves and to the reserves 

 in the rhizones through which the rapid growth becomes possible. 



Marked branches of individual trees of several common species were 

 kept under observation from February until May 1906, and with 

 the exception of Gilibertia and Turpinia none exhibited rapid growth. 



^Lock, R. H. On the Growth of Giant Bamboos. Ann. Roy. Bot. Gard. Peradeniya, 2, pt. 2, 

 August 1904. 



''Maxwell, W. The Rate of Growth of Banana Leaves. Bot. Centrb., 67, 1896. 

 'Schimper, A. F. W. Plant Geography, Oxford Edition, 1903, p. 218. 



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