ing to the formation of a concave rachis-segment type of 
fruit case. The similarity of end products in these two 
separate lines of evolution results from parallel tendencies 
for contraction, compression and reduction. The final 
product in the Hordeae series (Monerma cylindrica), does 
not quite approach the ultimate state of perfection as a 
protective device which is found in the American May- 
deae, because it lacks the increased protection provided 
by the lateral wings of an adnate prophyll. Thus, Mon- 
ermais more similar to Manisuris than it is to T’ripsacum. 
ACKNOWLEDGMENTS 
During the preparation of the manuscript, many help- 
ful suggestions were made by Professor P. C. Mangels- 
dorf of Harvard University and Professor E. Hernandez 
X. of the National School of Agriculture, Mexico. 
Specimens of the Gramineae in the Harvard University 
Herbarium were utilized for this study. 
[ 237 ] 
