56 



A MONTANE EAIN-FOEEST. 



On the shoots of Hedyosmum arborescens and of Podocarpus urbanii 

 which were under observation no new leaves were formed, although 

 the shoots were favorably situated as respects light and their position 

 on the tree. In Clethra and Viburnum the leaves which appeared 

 after the mid-winter defoliation of the trees grew less rapidly than the 

 leaves of Alchornea, which is in continual activity, and made in a week 

 about the same increase in size that may be made in a single day by 

 the leaves of a maple in the eastern United States in April or May. 



Owing to the slowness of shoot growth I have confined my measure- 

 ments to leaves. During the spring of 1906, from February to May, 

 I made determinations of growth rate in Boehmeria caudata, Alchornea 

 latifolia, Clethra occidentalis, Tovomita {Clusia) havetoides, Pilea nigres- 

 cens, and Cyathea pubescens.^ Additional measurements were made 

 in 1909, from July to October, The measurements at both times 

 were commonly made at fortnightly intervals. 



Table 13. — Maximum rates of leaf growth in rain-forest plants. 



The growth of each leaf is at first slow, reaches a maximum at about 

 one-fourth to one-half its mature size, and then falls to a much slower 

 rate. The most rapid maximum rates that were discovered in the 

 measurements of 1906 were 4.4 mm. per day for Boehmeria, 2.9 mm. for 

 Alchornea, and 49.4 mm. for the unfolding leaves of Cyathea. The 

 slowest maximum was for Pilea — 0.33 mm. per day. The measure- 

 ments of 1909 were made only on Pilea, Peperomia basellcefolia, and 

 Asplenium alatum. The maximum rates for all leaves measured in 

 1906 and 1909 are given in table 13. 



The fact that Pilea nigrescens is the commonest herbaceous plant 

 on the floor of the rain-forest, ferns excepted, and the fact that it 

 exhibited the slowest rate of growth of any of the plants brought 

 under measurement, led me to make a more extended series of observa- 



'Shreve, F. Kate of Growth in the Mountain Forests of Jamaica. 

 Circ. No. 195, March 1907. 



Johns Hopkins Univ. 



