e 
348 GENERAL MORPHOLOGY OF THE FLOWER. 
the two extremities of the embryo, which in such cases is 
generally peripherical, become also approximated, and it is said 
to be amplhitropous. Thus, when we wish to know the direction 
of the embryo, by ascertaining the position of the hilum, chalaza, 
and micropyle, it is at once evident. 
We have now lastly to explain the different terms which are 
in use to express the relations which the embryo bears to the 
cavity or cell in which it is placed. We have already described 
the terms used in defining the position of the seed to the same 
cavity (see page 334), which we found might be either erect, 
inverse, suspended, pendulous, ascending, or horizontal, in the 
same sense as previously mentioned when speaking of the ovule 
(page 326). But as regards the radicle this is said to be 
superior or ascending, as in the Nettle (fig. 779, r) and Rumex 
(fig. 780, 7), when it is directed towards the apex of the cell or 
pericarp ; wiferior or descending when it points to the base ; 
centripetal if turned inwards towards the axis or centre ; and 
centrifugal when it is turned towards the sides. The above 
relations of the embryo to the other parts of the seed and to 
the cavity or cell in which it is placed, are sometimes of much 
practical importance. 
Section 7. THEORETICAL STRUCTURE OR GENERAL MORPHOLOGY 
OF THE FLOWER. 
Havine now taken a comprehensive view of the different 
organs of the flower, we are in a position to examine in detail 
the theory which has been kept constantly in view in their 
description, namely, that they are all modifications of one 
common type,—the leaf. The germ of this theory originated 
with Linnzeus, but the merit of having first brought it forward 
in a complete form is due to the poet Goethe, who, as far back 
as 1790, published a treatise ‘On the Metamorphoses of Plants.’ 
The appearance of Goethe’s treatise at once drew the attention 
of botanists to this subject, and it is now universally admitted 
that all the organs of the flower are formed upon the same plan 
as the leaf, or, in other words, that they are homologous parts, 
and that they owe their differences to special causes connected 
with the functions which they have severally to perform. 
Thus the leaf, being designed to elaborate nutriment for the 
support of the plant, has a form, structure, and colour which 
are adapted for that purpose ; while the parts of the flower, 
being designed for the purpose of reproduction, have a structure 
and appearance which enable them to perform their several 
functions. 
It was formerly said that the parts of the flower were 
metamorphosed leaves, but this is stating the question too 
broadly, because they have never been leaves ; they are to be 
