Comparative study of the secondary phloem of some woody dicotyledons

The anatomical features of the secondary phloem of 444 species of woody dicotyledons, belonging to 24 families, all from the Ivory Coast, West-Africa, were used to find correlations among the different types of secondary phloem characteristics as indicated by Zahur (1959). Special attention is given to companion cells since according to Zahur (1959), the type is fairly constant for natural categories. A reinvestigation of Zahurs data also revealed some correlations not noticed by him. In the axial system of the secondary phloem of the investigated species both a primitive companion-cell type (type A) and in less extent a primitive sieve-tube type (type I) are associated and therefore correlated with an advanced axial-parenchyma type (type +) and mechanical-tissue type (type I). Also the reverse correlation is present. A correlation between a primitive companion-cell type and a primitive sieve-area type (type a) as one could conclude from Zahurs data, is not present in our material. Also the correlation between an advanced companion-cell type (type C) and an advanced sieve-area type (type c), is difficult to ascertain or entirely absent. The above described correlation is less evident or even absent in those species in which a primitive sieve-tube type (type I) is present together with an advanced companion-cell type (type C) and in those species in which an advanced sieve-tube type (type III) is present together with a primitive companion-cell type (type A). In the secondary phloem of the concerned species from the Ivory Coast this is rather often the case. If a storied structure is present sieve-tube type III occurs associated with companion-cell type C (and B). Such a combination of the two factors clearly indicates a primitive axial-parenchyma type (type -) and mechanical-tissue type (type 3), since both factors point in the same direction.