Le phloème de Lycopodium clavatum : organisation, ultrastructure et histochimie

Metaphloem sieve elements of Lycopodium clavatum L. are elongated cells with steeply inclined end walls. Numerous pores of small diameter are present on all contact walls between sieve elements. At maturity, these elements lack a normal-looking nucleus, and their protoplast is partially degenerated. Parenchyma cells with a well-structured protoplast are associated with them, the symplastic continuity between the two types of elements being assured by plasmodesmata. Intense phosphatase and respiratory enzyme activities are identifiable in the parenchyma cells. A functional association appears to exist between sieve elements and parenchyma cells.The absence of refractive spherules from the phloem of all the Lycophyta studied up to now is underlined: this fact is in agreement with the hypothesis that the Lycophyta constitute a relatively isolated group amongst primitive Tracheophytes.