272 
J. ARTHUR HARRIS AND JOHN V. LAWRENCE 
has seemed desirable to limit the determinations to those based on 
terrestrial plants. Epiphytic forms are reserved for treatment, with 
comparable forms from other regions, in a special publication. 
In a habitat in which erosion is so active, epiphytes are frequently 
brought to the ground by the fall of trees. Furthermore, conditions 
on the litter-coveied forest floor, on large fallen and partially decayed 
logs, and on the higher limbs of trees, differ by only imperceptible 
degrees. Thus our separation of the epiphytes from the terrestrial 
forms has of necessity been somewhat arbitrary. 
All of the Bromeliaceae we have omitted from the present treat- 
ment. 
Of the Orchidaceae we are publishing determinations for the terres- 
trial Prescottia stachyoides and Stenorrhynchos speciosum. Epidendrum 
verrucosum we have included since we always collected it growing in 
soil on rocky banks. Fawcett and Rendle give its occurrence as 
"on trees, rocks and dry banks." Epidendrum imbricatum, which 
Fawcett and Rendle cite as occurring on trees and which we found 
growing as a typical epiphyte, we have omitted from the present 
paper. The parasites have been discussed in an earlier number of this 
Journal (Harris and Lawrence, 1916). 
The species of the genus Peperomia have caused considerable 
trouble. They may be either truly epiphytic, rooted in the masses 
of leaf mould on fallen logs, or terrestrial in peaty soil. So far as we 
were able to observe P. stellata is always terrestrial. We have there- 
fore included it, but have reserved all other species of Peperomia 
for a special memoir on epiphytic vegetation. 
Blakea trinervia and Tradescaniia multiflora, which may be either 
rooted in the soil or epiphytic, have been included in this paper. 
Methods. — The methods employed were those of previous papers of 
this series. Considerable difficulty of a purely physical sort was 
encountered in the collection of the samples. Much of the work 
had. to be carried out in the rain or in tangled vegetation dripping 
wet from recent rain or fog. It was often necessary, therefore, for one 
worker to crouch under a poncho and wipe each leaf dry with absorbent 
tissue before it was placed in the collecting tubes for preliminary 
freezing (Gortner and Harris, 19 14). 
The frozen tissue was squeezed with the greatest thoroughness 
possible in a press with a powerful hand screw to avoid any possibility 
of the differential extraction of sap as noted by Dixon and Atkins 
(1913) and ourselves (Gortner, Lawrence and Harris, 1916). 
