Chap. V. 
COEKELATION OF GEOWTH. 
145 
difference in the ray and central florets for instance, 
the daisy, and this difference is often accompanied with 
the abortion of parts of the flower. But, in some Com- 
positous plants, the seeds also differ in shape and sculp¬ 
ture ; and even the ovary itself, with its accessory parts, 
differs, as has been described by Cassini. These differ¬ 
ences have been attributed by some authors to pressure, 
and the shape of the seeds in the ray-florets in some 
Composit 80 countenances this idea; but, in the case of 
the corolla of the Umbelliferse, it is by no means, as Dr. 
Hooker informs me, in species with the densest heads 
that the inner and outer flowers most frequently differ. 
It might have been thought that the development of 
the ray-petals by drawing nourishment from certain 
other parts of the flower had caused their abortion; but 
in some CompositsB there is a difference in the seeds of 
the outer and inner florets without any difference in the 
corolla. Possibly, these several differences may be con¬ 
nected with some difference in the flow of nutriment 
towards the central and external flowers : we know, 
at least, that in irregular flowers, those nearest to 
the axis are oftenest subject to peloria, and become 
regular. I may add, as an instance of this, and of a 
striking case of correlation, that I have recently observed 
in some garden pelargoniums, that the central flower of 
the truss often loses the patches of darker colour in the 
two upper petals ; and that when this occurs, the adhe¬ 
rent nectary is quite aborted ; when the colour is absent 
from only one of the two upper petals, the nectary is 
only much shortened. 
With respect to the difference in the corolla of the 
central and exterior flowers of a head or umbel, I do 
not feel at all sure that 0. C. SprengeFs idea that the 
ray-florets serve to attract insects, whose agency is 
highly advantageous in the fertilisation of plants of 
H 
