The three-dimensional structure of primary phloem systems.

A method has been developed for staining the phloem so that its ramifications can be observed directly in thick preparations. This method is based on clearing the material with lactic acid, staining with lacmoid and observing it in sodium lactate. Phloem anastomoses between the primary vascular strands of stem internodes were found to be common in many plant species (18 out 26 studied). These anastomoses are possible channels for the lateral distribution of materials in the stem and for movement of assimilates upwards from the leaves.