1900] LIFE HISTORY OF SILPHIUM 125 
Compositae which have been described. Eight chromosomes 
were counted in the megaspore mother cell. The number has 
not been reported for any other genus. 
Four of the five species studied — S. integrifolium, S. trifoliatum, 
S. terebinthinaceum, and S. laciniatum—resemble each other in — 
the general structure of the embryo sac. The synergids and 
oosphere are somewhat pear-shaped, the egg being inserted near 
the apex of the sac. The polar nuclei fuse before fertilization, 
and the definitive nucleus lies near the egg apparatus. The antip- 
odal cells are arranged in a row, and, as is common among 
Compositae, tend to increase in number beyond the original three. 
The growing sac quickly ruptures the nucellus, and the basal 
portion of the latter is to be found as a remnant by the side of 
the antipodal cells. The terminal portion generally remains 
perched on the apex of the sac, forming a densely staining cap. 
In one case these nucellar cells had continued their growth in 
this position. Such a nucellar cap is new for Compositae, but 
has been reported in various aroids by Campbell (30) and others. 
The embryo sac of S. perfoliatum is like that of the other 
Species in most respects, but presents a very different appearance 
in its micropylar portion. There is no nucellar cap. The syn- 
ergids are very much elongated, their tips being filled with a very 
dense protoplasm. They do not, however, rupture the tip of 
the ‘ 
The development of the microsporangia follows the well- 
known order, the steps of which need not be repeated. By the 
failure of the last series of divisions, the middle layer may be 
lacking, the sister layer to the tapetum in this case developing 
into the endothecium. The sporogenous cells divide at least 
Once after the tapetum begins to take a differential stain. 
The nuclei of the pollen-mother cells show a well-marked 
Synapsis stage, and pass quickly from this to the formation of 
the spindles for the first division. In the equatorial plate of this 
Spindle the reduced number of chromosomes, eight, was repeat- 
edly counted. The second division follows immediately after 
the first. 
