THE WOOD STRUCTURE OF SOME ARIZONAN AND CALIFORNIAN SPECIES OF CUPRESSUS

Abstract

The microscopic wood structure of nine species of Cupressus native to Arizona and California was studied from approximately 700 samples. Tracheid and ray cell dimensions, size and distribution of rays, size and arrangement of pits, and thickness of cell walls were found to vary in different parts of the tree, the trends resembling those in other Cupressaceae. Comparisons of the data relating to homologous wood samples revealed slight interspecific differences in mean values for some structural features, but the range of intraspecific variability was usually broad. No single microscopic character was discovered which alone could be considered reliable for species differentiation, but certain features such as the frequency of rays, size of crossing field pits, size of tracheids and ray cells, and thickness of ray cell walls may prove valuable for diagnostic purposes when used together. As in the case of morphological characteristics, species differentiation apparently rests upon slight differences in several characters rather than invariable or marked divergence in single features.