The elementary composition of the fungal vesicles of Trifolium pratense L. endomycorrhizas was determined using the laser-probe mass spectrography. Anatomical and cytological studies were also made so as to locate and describe the Endogonaceae in the infested roots of the host plant. Results obtained with fixed and unfixed samples are compared. The fixatives and embedding procedures are not convenient for elements such as potassium. It appears that the vesicles of the Endogonaceae, in addition to their high lipid contents could act as reservoirs for many elements, the principal elements detected being K, Ca, Mg and Na.