444 BOTANICAL GAZETTE [JUNE 
describes it for Ptelea trifoliata, and SOLEREDER® notes its appearance 
in several genera of the Saxifragaceae other than Philadelphus. It 
therefore occurs in widely scattered families and probably has but 
little taxonomic significance. 
SUMMARY. 
Among the more interesting points brought out by this study are 
the following: the early thickening of the cuticle; the variation in 
the number of epidermal hairs and stomata; the early formation of 
cork in regions exposed to the sun; the stone cells in the outer bark, 
between the strands of primary sclerenchyma, and in the inner bark; 
the regular layers of thick-walled phelloderm derived from the second- 
ary phellogens. 
The writer is indebted to Professor ALEXANDER W. Evans for 
criticism and advice. 
SHEFFIELD SCIENTIFIC SCHOOL, 
YALE UNIVERSITY. 
8 Syst. Anat. der Dicot. 360. 1899. 
