66 BOTANICAL GAZETTE [JULY 
filled except for occasional bubbles. Seen in transverse section a 
plate in a vessel appears as a thin imperforate membrane thickened 
in contact with the wall or with a rupture in the middle (fig. 4, c), 
presumably due to shrinkage. Exactly the same features charac- 
‘terize the resin masses in the tracheids of the gymnosperms. 
The presence of secretions (or excretions) in the tracheae only 
or in both tracheae and prosenchyma in the dicotyledons is very 
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Fic. 5.—Tangential section of Nyssa sylvatica 
common, and in a great many cases such material is in the form of 
a collar about the cell wall and with a diaphragm of greater or less 
thickness across the cavity. The writer believes that these various 
substances, although different in chemical composition, are alike in 
being excretions resulting from the metabolic activities of paren- 
chyma cells, and represent waste materials. Although produced 
in varying amount under normal conditions, the greatest production 
occurs when the cells are about to cease their vital functions and 
become heartwood, or when a similar condition is produced abnor- 
