this method of illustration.
There are various corollaries to this method of describing the form of a leaf which may be here alluded to, for we shall not return again to the subject of radial co-ordinates. For instance, the so-called unsymmetrical leaf9 of a begonia, in which one side of the leaf may be merely ovate while the other has a cordate outline,
is seen to be really a case of unequal , and not truly asymmetrical, growth on either side of the midrib. There is nothing more mysterious in its conformation than, for instance, in that of a forked twig in which one limb of the fork has grown longer than the other. The case of the begonia leaf is of sufficient interest to deserve illustration, and in Fig. 360 I have outlined a leaf of the large Begonia daedalea . On the smaller left-hand side of the leaf I have taken at random three points, a , b , c , and