Secondary Walls in Phloem of Pinus radiata D. Don

Abstract

Abbe and Crafts¹ showed that the development of secondary walls in the sieve cells of gymnosperms is apparently restricted to the Abietineae; there is no evidence of secondary wall in the sieve cells of Taxodineae, Araucarineae, Cupressineae and Taxineae. Moreover, the Abietineae develop no fibres, but the secondary walls of their sieve cells appear to be composed of relatively pure cellulose. Secondary walls occur in the sieve cells of white pine, Pinus strobus L. (Figs. 3 and 24 in ref. 1).