Leaf Production and Morphology in the Artichoke Gall of Yew (Taxus baccata L.)

Comparative leaf production rates and leaf morphology studiesfor galled and normal shoots of yew trees have been obtainedthroughout the life cycle of the causative agent, the gall midge,Taxomyia taxi. Normal and galled shoot leaf numbers have beenrelated to those of their parent shoots. It was found that whereasthe annual leaf production of normal shoots was positively relatedto that of the parent shoots, galled shoot leaf production remainedconstant regardless of parent shoot vigour showing leaf stimulationby the midge to be a special case. The midge larva appears tobe determining the rate of leaf production in galled shoots.In galls leaf production continues throughout the winter monthswith no dormant period. From morphological evidence, alternationof leaves and cataphylls is continued in galled buds.