The proportion of sieve elements in the phloem of some tropical trees.

Measurements have been made of the proportion of the area of sieve elements in the cross-sectional area of the secondary phloem of trees of two tropical genera in which the presence of storied sieve plates makes the recognition of sieve elements particularly easy. This proportion, often accepted as one fifth in the literature on phloem and translocation, rises as high as three quarters in one of the trees measured.