84 INTRODUCTION 
others. The ray-florets are usually ligulate, by which the end in view is attained 
even more successfully. The enlargement of the marginal flowers of an inflorescence 
also occurs in the corymbs of some Cruciferae (Iberis), and in many Umbelliferae 
(Daucus, Heracleum, Anthriscus, Conium, Orlaya, and others). 
In many cases there is a division of labour between the flower of an in- 
florescence: the inner ones are sexual, and devoted to reproduction, the outer 
are asexual, and have undergone a great development of the parts that serve for 
attraction, at the expense of stamens and carpels. Instances are afforded by 
Centaurea, Viburnum Opulus, and others. It sometimes happens that the upper 
flowers of an inflorescence serve to attract, while the lower ones are concerned 
with reproduction. In Muscari comosum, for example, the compressed ear-like 
inflorescence is only a few centimetres in length at the time of budding. Later 
on, by gradual extension of the axis, it develops into a raceme of 20-30 cm. long, of 
which the uppermost twenty to thirty flowers remain infertile, but assume a deep blue 
colour, and are borne upon similarly coloured upwardly directed stalks of 1-2 cm. 
in length. The (sessile) buds are also blue, but the open flowers with stamens and 
carpels, about thirty to forty-nine in number, are coloured brown, and arranged in a 
very loose and inconspicuous raceme (Knuth, ‘ Bliitenbiol. Beob. auf d. Insel Capri,’ 
Bot. Jaarb., v, 1893, pp. 25-7). 
Many inflorescences develop flowers on one side only. This is most strikingly 
seen in racemose inflorescences, e. g. Digitalis purpurea, Teucrium Scorodonia. If 
the flowers were arranged regularly around the stem, they would be much less 
conspicuous than they are when arranged unilaterally, although with this latter 
arrangement they are only visible to insects coming from one side. Such in- 
florescences, however, possess the further advantage that their insect-visitors, chiefly 
bees, ascend them with the greatest regularity, as if on the steps of a ladder, 
without passing by a single flower, as is very often the case in radially symmetrical 
inflorescences, with the result that some flowers often remain unfertilized. 
J. Urban (Ber. D. bot. Ges., Berlin, iii, 1885, pp. 411 et seq.) calls attention to 
the fact that one-sidedness in inflorescences is brought about by various causes, 
namely :— 
1. By curvatures of the flower-stalks. This is the case, e.g. in Digitalis 
purpurea Z. The bracts and flower-stalks are here regularly arranged around 
the floral axis; but while the former retain their original position, the latter bend 
to one side in such a way that the outermost flowers diverge 80-120°, making 
the inflorescence unilateral. Owing to this arrangement the flowers are adapted 
for cross-pollination by insects with the least possible loss of time, and visits are 
secured. They present a striking appearance on one side only, though on this 
side they are highly conspicuous. This disadvantage is compensated by the fact 
that the lateral inflorescences developing below the terminal one always turn the 
side devoid of flowers towards the main axis. Even neighbouring plants are 
similarly related to one another, for the outer inflorescences turn their flowers 
outwards, quite independently of the strength or feebleness of the illumination. 
In Scutellaria peregrina Z. and other species of the same genus, the markedly 
unilateral arrangement of the flowers is chiefly caused by curvature of the flower- 
stalks, combined with bending of the leaf-stalks. 
