vi Preface 
by Massee (Duckworth & Co.), and Figs. 46 and 21 
from Percival’s Agricultural Botany (Duckworth & Co.). 
My thanks are due to Prof. Biffen and the editors 
for suggestions and criticisms and to the above- 
mentioned authors and publishers for kind permission 
to reproduce certain illustrations. 
F. RB. P. 
ScHoot or AGRICULTURE, 
CAMBRIDGE. 
March, 1916. 
