61 
Cistus are near together. Their separation must be considered a 
peculiarity of the Engler System. It is, in fact, indicated by 
Iengler in his own diagram published in 1897, that these groups 
are closely related. 
— 
With such a large number of families united by parietal placen- 
tation and other characteristics—such as numerous stamens, sepa- 
rate sepals, frequent spiral arrangement of parts—the question of 
the relation of the various forms of placentation assumes special 
interest. Parietal placentation in the bud often changes to axile 
in the flower: the opposite is never the case. In the Introduction 
to his famous Syllabus, Engler wrote: * 
now established in its principal features. 
The natural system 1s 
When one examines 
recent systems of classification of dicotyledons the words, “ prin- 
cipal features,” must be used in a broad sense to make the state- 
ment a true one. The early systems were linear ones. Systems 
of dicotyledons with a branching arrangement, indicated by dia- 
grams, have been published by Engler 1897, Wettstein 1911 and 
1923, Bessey 1914, Hutchinson 1926, and others. Comparing 
these diagrams we get a good idea of differences; we see, at the 
same time, that there is also substantial agreement on many points. 
lor example, differences regarding the Sympetalae are compara- 
tively slight. 
It is not to all characters of floral structures, but to those having 
a bearing on these differences of opinion that I have given atten- 
tion in the study of flowers and their development, and with special 
reference to groups other than Sympetalae. Among these groups 
greater attention to placentation simplifies the classification. 
SYSTEMATIC BoTANY 
By Henry K. SvENSoN 
During the spring of 1936 three weeks were occupied in plant- 
collecting in Tennessee. The following studies have been com- 
pleted or are under way. 
1. Ferns of the Galapagos and Cocos Islands. <A detailed re- 
port, of which the manuscript 1s nearly finished. 
2. Report on the sedges of the Crocker [¢xpedition to the Gala- 
pagos and Revillagigedo Islands, and western Mexico. 
