1900] LIFE HISTORY OF SILPHIUM 105 
which I found, the nectary was in each case below the stamen 
(fig. 24). It is hardly conceivable that the nectary of the ray 
flower is formed from an outer stamen whorl, not yet completely 
lost in the genus, while in the disk flower it comes from an inner 
set which is absent in all the tetracyclic Sympetalae. It is much 
more reasonable to regard the nectary as an organ of independ- 
ent origin. 
DEVELOPMENT OF THE MEGASPORE AND EMBRYO SAC. 
When the ovule has reached the stage shown in jig. 22, the 
hypodermal archesporium is easily recognizable at the end of an 
axial row of cells (fig. 28). Its cytoplasm is finely granular, 
and its nucleus has already left the resting condition, showing a 
continuous spirem thread along which the chromatin granules 
are arranged. /ig 29, from an ovule of about the age of the 
one in fig. 23, shows the nucleus with a prominent nucleolus 
and eight bodies of a different staining reaction, the chromosomes. 
There is as yet no trace of a spindle. In fg. 30, taken from the 
ovule outlined in jig. 24, the equatorial plate is fully formed. A 
complete count of chromosomes was not possible here, owing to 
their being so closely crowded together. Six were plainly visi- 
ble, and a comparison with fig. 29, and with the corresponding 
division of the pollen mother cell ( fig. 54), leads certainly to 
the conclusion that eight is the characteristic reduction number. 
I have made no accurate count of the chromosomes in other 
tissues, but dividing nuclei found in the large tapetal cells appear 
to have many more than eight, probably sixteen. 
Guignard (15) describes the reduction division in the ovule 
of Allium ursinum as occurring in the archesporial cell, which 
here produces a row of four cells, the innermost of which devel- 
ops into the embryo sac. A similar condition has been reported 
by Strasburger for Alkium fistulosum and Helleborus foetidus (16). 
Such a row of four cells is formed in Silphium (fig. 37), as 
indeed in all the Compositae which have been examined. In the 
determination of the homologies of the cells thus produced, as 
well as that of the original hypodermal cell, the reduction 
