1900 | LIFE HISTORY OF SILPHIUM 101 
ORGANOGENY OF THE FLOWER. 
On account of the difference in the development of the disk 
and ray flowers, it is necessary to consider the two separately. 
It has been found, also, that a clear understanding of the sequence 
and relations of the organs in the disk flowers assists greatly in 
the interpretation of the more irregular development of the ray 
flower. 
Disk flowers.—The earliest appearance of the disk flowers 
upon the receptacle is shown in fig. z, the broader protuberance 
(@) being the receptacle of the individual flower, and the nar- 
rower one (ér,) the subtending bract. A second bract (dr,) is 
just appearing. Just before the appearance of the first floral 
organs the receptacle is of the form shown in fig. 2, d,, being 
somewhat broader than high, and very symmetrical in outline. 
The outline of the receptacle soon becomes angular by the 
upward growth of a marginal ring (fig. 2, d,, fig. 3), which is 
the beginning of the corolla tube. In fig. ¢ the corolla tube has 
begun to curl inward over the top of the flower, and an inner set 
of five hemispherical protuberances (sé), the young stamens, 
have appeared. The appearance of the carpels (4, figs. 5, 6) is 
accompanied by a broadening of the receptacle, which regains 
its original proportions as the stamens and carpels acquire a more 
erect position (figs. 7, 8). 
In figs. 7 and g a notch may be seen on each side at the 
base of the corolla; just above an annular swelling. This ring 
marks the position of the calyx, which soon appears (fig. I0, pa) 
as a rudimentary pappus of two or three whorls of short hairs, 
each hair consisting of about three cells (fig. zz). The nectary 
consists of a ring around the base of the style (jig. 9, ). 
Martin’s account for Aster and Solidago (19) agrees in a 
general way with the account of Silphium here given. However, 
he finds the calyx in those forms arising much earlier, in fact 
almost simultaneously with the stamens. 
It is well known that in many Compositae the base of the 
Style is spirally coiled, and the straightening of this spiral at 
Maturity constitutes the stylar thrust by which the pollen is 
