216 EVOLUTION OF PLANTS 
the great family of Composite is the highest of all. 
The latter is the largest family of plants and shows 
extreme specialization of the floral structures in the ex- 
tensive cohesion of the parts, which extends to the sta- 
mens as well as the other parts of the flower. The 
flowers, as is well known, are aggregated in dense heads 
surrounded by bracts which give the whole inflorescence 
the appearance of a single flower (Fig. 53, E,G). This 
is especially so in such forms as the asters and daisies, 
where the outer flowers have the corolla large and flat- 
tened, so that each of these “ray-florets” looks like a, 
single petal. In many genera these outer flowers are 
destitute of stamens and sometimes the pistil is also 
abortive, and the ray-florets serve simply to make the 
inflorescence conspicuous. There are many interesting 
transitions between the lower Composite, where all the 
flowers of the inflorescence are alike, and those in which 
the ray-florets are entirely sterile. 
The type of inflorescence developed in the Composite 
seems to have been particularly effective, as these plants 
are notoriously prolific. The actual number of seeds is 
not excessively large as compared with many other 
plants ; but each individual flower almost always suc- 
ceeds in ripening its seed, and the one-seeded fruits are 
usually provided with most efficient means of transpor- 
tation. One has but to think of the legions of common 
Composites, — daisies, sunflowers, thistles, burdocks, 
dandelions, and many others of our commonest and 
most troublesome weeds,—to realize how well fitted 
these plants are to hold their own in the struggle for 
existence. 
