PREFACE. 
I Have placed the essays. in the order in 
which they will be found in accordance with 
the dates when they were first published. As 
I wish to acknowledge to whom I am indebted. 
for the permission to reproduce them, and also 
wish to refer my readers to the originals in 
case they should wish to consult them, | 
cannot do better than to thank, the journals, 
and to give the necessary list at the same 
time, as follows :— 
(1) Dr. Axel Preyer's article will be found 
in Der Tropenpfianzer, No. 4, of April, 1901, 
pp. 157-173. The translation, made by my 
brother Victor and M. Ulrich Hugentobler, . 
originally appeared in Zvopzcal Life. 
(2) Dr. Oscar Loew’s essay is taken from 
Bulletin No. 1093 of the United States 
Department of Agriculture (Office of Experi- 
-ment Stations), and first appeared in the 
Annual Report of the Porto Rico Agricultural 
Experiment Station for 1907. 
(3) Dr. Fickendey’s (Director of the 
Experiment Station, Victoria, Cameroons, 
German West Africa) was taken from 
Der Tropenpflanzer, No. 2, of February, 
1909, pp. 87-90; and I am indebted to 
