296 CAIN, DE OLIVEIRA CASTRO, PIRES, AND DA SILVA 



the flora is so rich, the densities of trees of a species so low, and the domi- 

 nance so low and variable, that estimations of relative importance are nearly 

 if not actually impossible. The use of the importance value index, how- 



% 

 701- 



60 



50 



40 



30 



20 



10 







LE 



MES 



Ml 



NA 



MUCAMBO 

 RAIN, FOREST 

 BELEM, PARA 



LOG BASED RAUNKIAERIAN 

 LEAF-SIZE DISTRIBUTION 



MAC 



MEG 



25 



mm 



2.2 



20 



182 1640 

 sq cm 



ARITHMETIC -BASED DISTRIBUTION 



25 50 75 100 150 175 200 225 250 cm'^ 



Fig. 3. Percentages of species of trees of terra firme rain forest at Mucambo, 

 Belem, Para, having leaves of different sizes. Plotting in the upper histogram is 

 according to the leaf-size classes of Raunkiaer (see text) and in the lower diagram 

 is according to equal-sized classes. 



ever, permits the arrangement of all species in a linear series according to 

 the values of their indexes. We believe that the introduction of this concept 

 in phytosociological work in the tropics is very important. 



Our data on life forms do not need discussion at this point, but there are 

 certain points about the leaf-size study that should be exposed. In addition 



