IN VASCULAR PLANTS 207 
In accordance with the general opinions already expressed, it will 
be natural to take first into consideration the fertile region or strobilus: 
or in the higher plants the flower, which is held to be its outcome 
in a’ more advanced state of development. These may, according to 
a theory of sterilisation, be held to retain the primitive character of 
fertility: it will be seen that they are conservative also in their 
symmetry. 
It has become almost a commonplace of the elementary text-books 
that the radial type of flower in the Angiosperms is the primitive and 
the dorsiventral (or zygomorphic) the derivative condition. The ques- 
tion of symmetry of the flower has been treated so lately and so well 
by Goebel! that it is unnecessary here to discuss it in detail. He 
distinguishes two cases: first, that in which the flowers are laid down 
radially, and become dorsiventral in the course of development—this 
includes most of the dorsiventral types, and various influences may be 
recognised as conducing to the result, such as the unequal incidence of 
gravity and of light. Secondly, he distinguishes that type in which 
dorsiventrality is brought about before the unfolding of the flower. In 
this case he is of opinion? that we have in the position of the flower 
an element of special importance, and the behaviour of the flower in 
becoming dorsiventral only after unfolding must be taken as a starting- 
point in any enquiry into this matter. Lateral flowers are in a different 
position with regard to external forces from terminal flowers. According 
to the sensitiveness of the former to external factors the configuration 
of the flower will be changed more or less early. Such changes may 
become inherited, and flowers so changed will be, of course, favoured 
over others, and many of their parts will be aborted as useless members 
after the introduction of dorsiventral structure. In this connection the 
fact is of importance that in plants normally with zygomorphic flowers, 
when a terminal flower appears, it is frequently of radial type, or is, as 
it is termed, peloric. Goebel remarks,? “No doubt these wonderful forms 
of flower exhibit a more primitive type than the dorsiventral flowers, 
which are the normal ones in the plants in which they occur.” Experi- 
ment has shown in certain cases that peloria is related to intensity of 
insolation, and thus it seems not impossible that the quality of the light- 
ing, as well as position, may have had its influence in leading to 
zygomorphy. But whatever the conclusion drawn from a complete 
analysis of the causes leading to zygomorphy may be, that analysis, as 
far as it has gone, and comparison also, point clearly to the radial type 
of flower in Angiosperms as the primitive, and the dorsiventral as the 
derivative. Similarly, in the case of inflorescences, which are often dorsi- 
ventral in their development, it may be held as probable that the 
dorsiventral inflorescences have proceeded from radial ones.* 
1 Organography, Engl. edn., vol. i., p. 128. 22.0, p. 132. 
%Z.c., p» 188. *Goebel, /.c., p. 138. 
