The predictive value of the vessel element features of fossilized, sma
ll diameter dicotyledonous angiosperm axes for palaeoecological recons
tructions is investigated. The Vulnerability Index and Mesomorphy Rati
o have been employed. Anatomical distinctions between young twigs, bra
nches, main axes and roots of Betula pendula Roth, Aesculus hippocasta
num L. and Poplus nigra L. were established so that the problems in ex
trapolating such formulae, based on branch wood, to twig wood could be
overcome. The variations in anatomy and thus discrepancies in the val
ues obtained from these two parameters, between mature and juvenile wo
od, are discussed and correction factors devised to enable the derivat
ion of these parameters directly from the twig material. Modified vers
ions of the Vulnerability Index and Mesomorphy Ratio have then been ap
plied to the pyritized ''twigs'' of the London Clay. A palaeoclimatic
signal for the southeast of England has been obtained and its reliabil
ity is then discussed.