A method for estimating the proportion of sieve tubes in the phloem of higher plants.

A statistical method has been developed for the estimation of the proportion of phloem area occupied by sieve tube lumen which is applicable to most higher plants. By simple probability, the number of sieve tubes in a given area of phloem is equal to the number of sieve plates present in a series of transverse sections whose total thickness equals the mean sieve element length. The case of oblique sieve plates, where the plate is divided and occurs in more than one section, has also been dealt with and a solution obtained. Estimates of the proportion of phloem area occupied by sieve tubes have been made by this method in willow (Salix viminalis L.), sugar beet (Beta vulgaris L.) and a cucurbit (Ecballium elaterium L.) and the values obtained discussed in relation to estimates made previously by other methods.