Scanning electron photomicrographs of transverse sections of control and symptomatic beech (<i>Fagus grandifolia</i>) leaves.

(A) Transverse section of a control leaf showing the typical composition of six layers of cells. (B) Transverse section of a crinkled leaf (early spring) showing an abnormal number of cell layers and very compact intercellular spaces in the spongy mesophyll. (C) Representative transverse section of a symptomatic leaf showing asymptomatic (left) and BLD symptomatic (right) areas. (D-E) Symptomatic BLD section with numerous nematodes (arrows) within the spongy mesophyll. Scale bars: 20 μm (A, B); 100 μm (C-E).