Origin and Development of the Composites. 203 
investigation of the phyllotaxis are the proof of the primitiveness 
in the family of alternate phyllotaxis in the cauline leaves, and the 
elucidation hy Church’s work of the rules governing the number of 
rays and the general symmetry of the capitulum. 
Fruit Dispersal. Winds of comparatively small velocities are 
proved to be sufficient to disperse pappose fruits to any distance 
under proper conditions of atmospheric humidity. A method and 
a formula are given for calculating from the rate of fall in quiet 
air the minimum wind necessary for the dispersal of pappose 
fruits. A new type of anemometer of considerable accuracy is 
described. New experimental methods for determining the rate 
of fall in quiet air and the minimum wind necessary for dispersal 
are given. The hydrodynamics of the wind-dispersal of pappose 
fruits are elucidated. 
A preliminary explanation is given of the general phenomenon 
of the elongation of the stalk of the fruit or spore-sac which in 
most cases immediately precedes fruit- or spore-dispersal. This 
explanation is also applicable to the elongations of the axis which 
take place in the female cone of Finns. 
Geographical Distribution. The previous phyletic conclusions 
and the validity of the Law of Age and Area are confirmed by the 
geographical distribution of the species, genera and tribes of the 
family. The principle of physiological differentiation and restriction 
of area is elucidated. Other points illustrated are the irreversi¬ 
bility of evolution, the development of peculiar types in each 
well-defined climatic region, the correlation between ecological 
conditions and the vegetative forms assumed in the various tribes, 
and the existence of definite centres of origin and paths of migration 
for the various tribes. 
The explanation (Chap. X, A) of the espalier and cushion 
forms of plants by permeability changes which are directly due 
to the environment is of particular interest, since this view of 
epharmosis is capable of extensive development both experimentally 
and theoretically (cp. Chap. Ill, D, and Bib. Ill, 49 - 50 , and X, 68a). 
Origin of the Composites. It is shown to be highly probable 
that Senecio originated from the Lobelioideae by orthogenetic 
saltation and epharmosis in late Cretaceous or early Tertiary times 
in a particular region of South America. An eclectic theory of 
evolution is suggested and a close analogy is traced between 
orthogenetic saltation and the disintegration process of the radio¬ 
active elements, 
