IOWA ACADEMY OF SCIENCE 
*95 
CONCLUSIONS. 
From the foregoing, it is seen that there is quite a degree of uni- 
formity of variation for plants of a given species, from different 
localities. Had the number of variates from each locality been 
larger, it is very probable that the variation for localities would 
have been still less. 
Rudbeckia hirta and R. triloba are interesting when brought 
together in a study of this nature, because they are so closely 
related. In Gray’s “Synoptical Flora of North America,” Vol. I, 
Part II, 260-261, R. hirta and R. triloba are represented as very 
closely related to each other, and to R. bicolor and R. subtomen- 
tosa. It would be interesting to study the variation of these re- 
lated species, presenting as they do, no marked structural differ- 
ences. If the material were taken from the native habitats of the 
plants, many interesting facts might be brought out. 
There is some indication of a tendency to the formation of two 
somewhat distinct species from Rudbeckia hirta. In the dry, 
unfavorable soil, the predominating number of rays was 8, while 
the predominating number in good soil was 18. In the poor soil, 
the plants were small, and many bore but a single head. 
There also seems to be a tendency for the number of rays per 
head, of Rudbeckia hirta, to decrease, because the slope of the 
upper side of the frequency curve is steep, while the lower side 
is more gentle (Plate I). 
The tendency seems to be for the number of rays per head, of 
Rudbeckia triloba, to decrease a little. It is probably almost sta- 
tionary (Plate V). 
The tendency seems to be for the number of rays per head, of 
Helianthus grosse-serratus, to increase. The lower side of the 
curve is quite steep, while the upper is a more gentle slope (Plate 
VI). 
The results for Rudbeckia hirta in this study agree somewhat 
closely with those found by Lucas. Taking five groups, contain- 
ing from 173 to 318 heads each, he found the means to be 14.188, 
11.328, 11.868, 9.612, and 11.813. That all of his means are not 
very nearly 11.000, may be due to the small number of heads in 
each group. As has been indicated, the modes found in this study 
agree very closely with those indicated by him. 
No account has been taken of the period of the flowering season 
that these heads were counted. Undoubtedly, heads blooming 
earlier would vary somewhat from those blooming later in the 
