5° BOTANICAL GAZETTE [JULY 
marginal cells have disappeared from the xylem although not from 
the phloem. This and other observations indicate that phloem is a 
more conservative region than xylem. 
UNIVERSITY OF MAINE 
Orono, MaIne 
LITERATURE CITED 
1. Battey, I. W., Anatomical characters in the evolution of Pinus. Amer. 
Nat. 44: 284-293. pl. 2. 1910. 
» A Cretaceous Pityoxylon with marginal tracheids. Annals of 
Botany 25*315-325. pl. 26. 1911. 
3- JEFFREY, E. C., and Curyster, M. A., On Cretaceous Pityoxyla: Bor. 
AZ. 4231-15. pls. I, 2. 1906. 
4. PENHALLow, D. P., A manual of the North American Gymnosperms. 
Boston. 1907. 
5. STRASBURGER, E., Uber den Bau und die Verrichtungen der Leitungsbahnen. 
8o1. 
6. , Lehrbuch der Botanik. Neunte Auflage. Jena. 1908. 
7- THompson, W. P., The origin of ray tracheids in the Coniferae. Bor. GAZ. 
50: 101-116. 1910. 

2. 

