188 
IOWA ACADEMY OF SCIENCE 
Fig. 1. — Cross section, through portion 
entirely coated. 
Fig. 2. — Cross section, through portion 
partially coated. 
Fig. 3. — Cross section, through needle near 
base where no perceptible amount of tarry 
material was present. 
Fig. 4. — Normal. 
Fig. 5— Acetylene (1-6750) 
4 days. 
Fig. 6.— Acetylene (1-6750) 
4 days. 
Fig. 7. — Acetylene (2-7750) 
4 days. 
Figs. 1-3. — Cross sections of a Pine needle taken from Washington Park, Chicago. 
Figs. 4-7. — Pleurococens vulgaris. 
