CONSPICUOUSNESS OF FLOWERS 85 
In Salvia lanceolata Willd., the unilateral arrangement is brought about by 
twistings and flexures of the flower-stalks only, while the leaves maintain their 
position. Most of the Orchids develop one-sided inflorescences in a similar fashion. 
2. Unilaterality also results from curvature of the flower-stalks in 
compound inflorescences, e.g. in various species of Polygonatum and in 
Scrophularia lateriflora Zrau/v. As in these species most of the flowers are covered 
by leaves, and are therefore very inconspicuous, this floral arrangement must either 
be an adaptation to special agents of pollination, or must have some unknown 
oecological purpose. A contrast to these cases is afforded by the unilateral 
inflorescences of Elsholzia Patrini Garcke, which also come under this heading, 
and which are so conspicuous that they are obviously adapted to insect visits. 
3. Unilaterality of the inflorescence is conditioned by the nature 
of the symmetry. The leaves and flowers of all species of Gladiolus are 
primarily distichous. The kind of symmetry possessed, combined with slight 
torsions and curvatures, produce a markedly one-sided arrangement. 
4. Unilaterality of racemes is brought about by suppression of 
the flowers on one side of the axis. Examples:—species of Vicia (V. pisi- 
formis Z., tenuifolia Roth, V. Cracca Z., and others), also the species of Lathyrus, 
which are admirably adapted to their habitat, and to the visits of insects. If their 
inflorescences were developed on all sides, the marginal flowers at the back of the 
cluster would be seldom or never visited by insects. 
5. Unilaterality of uniparous cymes, whether these are pure or 
have arisen by reduction, is characteristic of the Boraginaceae, and so forth. 
6. Apically unilateral inflorescences include capitula and umbels in the 
widest sense, and these are characteristic for whole families. 
Urban makes the following oecological deduction from his observations :-— 
in a single branching plant, or in several that are near neighbours, the inflorescences 
turn their flowers outwards in one direction, i.e. away from the centre. The result 
is a common inflorescence exposed on all sides, and sometimes shared by various 
individuals. It therefore follows that conspicuousness with reference to insects 
approaching from a distance is greatly increased, and in the case of inflorescences 
which have become unilateral by suppression, there is economy of material without 
sacrifice of conspicuousness. And further, the oecological law for flowers—that 
the same end can be reached by the most varied means—is equally applicable 
to unilateral inflorescences. 
Conspicuousness is increased in many flowers by colour-contrast. This may 
be exhibited either by single flowers, as in the pansy (Viola tricolor), Linaria 
Cymbalaria, Myosotis palustris, Vicia faba, Narcissus poeticus, and others, or it may 
be between flowers and bracts, e.g. the golden yellow corolla and the deep blue 
bracts of Melampyrum nemorosum; or again the contrast may be between the 
different flowers of an inflorescence, e.g. the blue ray-florets and the yellow disk- 
florets of asters, and the like. 
It is also a highly remarkable phenomenon that, in some plants, the flowers 
persist for a considerable time after blooming, assuming a more intense colour 
than they previously possessed. In this way the conspicuousness of the whole 
