I 



FOREWORD ix 



were obtained from various sources, due credit 

 being given in each case. 



In the preparation of the manuscript and a 

 number of negatives the authors are indebted to 

 Mrs. A. F. Conradi for valuable assistance. 



A. F. C. 

 W. A. T. 



CLEMSON COLLEGE:, S.C. 

 June 1, 1916. 



