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



Table 17. Percentage of compotind leaves in the height sub-classes of phanerophytes 



in the Mucambo flora 



Pires et al. (1953) published a list of trees observed on a 3.5-hectare plot 

 in luxuriant, Virginia terra firme rain forest near the village of Tres de Outu- 

 bro, between Castanhal and the River Guama, east of Belem, Para. In 1955 

 the senior author of the present paper was able to study herbarium sheets 

 of 150 of these species at the Instituto Agronomico do Norte, Belem, through 

 the courtesy of Dr. G. A. Black, and computed the areas of typical leaves of 

 mature trees. All the tree species of the Castanhal study were included in so 

 far as they were represented in the herbarium, and where possible the Cast- 

 anhal material was used. The result showed that 74 per cent of the species 

 had leaves in the mesophyll-size class. It was not possible to separate the 

 species into life-form classes, but the data allowed the distinction of species 

 represented on the plot whose trunks were 40 cm. or more in diameter from 

 the total that was 10 cm. or more in diameter. Comparing the larger trees 

 with the total list, it was found that 16.6 per cent and 10.0 per cent were 

 microphyll, 71.1 and 74.4 per cent were mesophyll, and 3.3 and 12.2 per cent 

 were macrophyll. Very small percentages were in the other classes. 



Further analysis of the leaves of trees in the Castanhal study showed that 

 69.3 per cent are simple, 24.7 per cent are once-pinnate, 3.3 per cent are bi- 

 or tri-pinnate, and 2.6 per cent are palmate-lobed or divided. Considering 

 only the 37 species that are pinnate, 24 (64.9 per cent) are of mesophyll leaf 

 size, 11 species (29.7 per cent) are microphyll, and 2 (5.3 per cent) are 

 macrophyll. In the determination of leaf-size class of compound leaves, the 

 leaflet is taken as the unit, not the entire leaf, on the assumption that the 

 leaflet is the physiological unit responding to the conditions of environment 

 in correspondence with the simple-bladed leaf. Also in computing areas the 

 petiole is ignored and only the blade is measured. Of the five species with 

 decompound leaves, the leaflets were all small, three being leptophyll and 

 two being nanophyll. The four species with palmate leaves had two with 

 mesophyll leaflets and two with macrophyll leaflets. 



In the present study of Mucambo there were found to be 46 species with 

 compound leaves. On a basis of leaflet area, 4 species (8.7 per cent) were lepto- 



