298 



CAIN, DE OLIVEIRA CASTRO, PIRES, AND DA SILVA 



Table 14. Frequeticy of species in arithmetic leaf-size classes, terra firme rain 



forest, Para 



may be as large as many of the simple leaves, there is some tendency for 

 leaflets to average smaller than simple leaf blades in this vegetation. 



One of the conspicuous features of the leaves of tropical trees is their pre- 

 dominantly entire margins and lack of lobing. Also acuminate leaf tips are 

 very common. Among the Castanhal species we found 70.6 per cent with 

 acuminate tips. Furthermore, 28.0 per cent of the 150 species studied had 

 abruptly more or less long tips of the "drip-point" type. Leaf-tip analysis 

 was not made of the Mucambo species, but it is our impression that drip 

 points are very abundant on the leaves. 



The degree of floristic relationship between the two samples of terra firme 

 rain forest, Mucambo near Belem and Castanhal about 120 km. eastward, 

 is not very great. There are 11 families found only in the Castanhal sample, 

 3 families only in the Mucambo sample, and 36 families common to the 

 two. At the generic level there are 72 genera found only at Castanhal, 42 

 found only at Mucambo, and 58 genera common to both. Among species 

 133 were found only at Castanhal, 117 only at Mucambo, and 40 common 

 to both. The degree of similarity can be expressed in this way: 72 per cent 

 of the families are in common, 34 per cent of the genera, and only 14 per cent 

 of the species. In making these calculations it was necessary, of course, to 

 om.it those taxa in which the specific or generic identities are unknown. 



The vast majority of the genera are represented by a single species, and 

 thsre are only a few large genera. Protium (Burseraceae) has 20 species in 

 the combined lists, Pouteria (Sapotaceae) has 17 species, and Licania (Rosa- 



