A CONTRIBUTION TO THE LIFE HISTORY OF 
SILPHIUM. 
CONTRIBUTION FROM THE HULL BOTANICAL 
LABORATORY. XVII. 
WILLIAM DAYTON MERRELL. 
(WITH PLATES I1I—x) 
INTRODUCTION. 
THE flowers of Compositae are favorable for morphological 
study, in that several closely connected stages may be obtained 
in a single section. The broad outlines of the organogeny of 
the flower were early discovered, and it has only remained for 
later investigators to examine the more minute details. 
Aside from an interest in the family as being the highest 
among dicotyledons, the division of labor among the flowers of 
a head deserves attention. This is carried so far in Silphium 
that the ray-flowers ‘are ovulate and without stamens ; while the 
disk-flowers are staminate and without ovules, the style never 
forking. It might be expected that some transitional stages in 
the abortion of stamens or of ovules could be found, and the 
present study was undertaken with that in view. The results 
obtained in this particular were very meager, but the investiga- 
tion led to the discovery of several unexpected phenomena, 
which are herewith presented. 
MATERIAL AND METHODS. 
The material was collected during the summers of 1896, 
1897, and 1898, in the vicinity of Chicago. Unfortunately, most 
of the collections had to be made in the latter part of the day, 
and this probably accounts for the small number of cells found 
in process of division. Even in the youngest buds it was found 
to be advantageous to pick off the outer involucral scales, partly 
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