42 INTRODUCTION 
in the evening, Among Tubuliflorae, Geitonogamy is comparatively rare. In 
Eupatorium cannabinum (see Fig. 2), and in other species of this genus, the branches 
of the stigmas of the older florets of a head separate so widely that they touch 
the pollen-covered hairs of the neighbouring florets, which are just beginning to 
open. In Tussilago, when the head closes in the evening, the pollen emptied 
out of the anther-tubes of the disk-florets is transferred to the ligulate ray-florets. 
When the head opens again, the pollen slides down the ligulate corollas to the 
stigmas situated at their bases. In Calendula, the style-branches of the ligulate 
ray-florets curve over the pollen-covered disk-florets, and thus get pollinated. In 
the Asterineae (Aster, Solidago, &c.) the pollen of the disk-florets falls on to the 
already mature stigmas of the ray-florets, in consequence of the inclination of 
the heads. In many Compositae (Homogyne, Artemisia, Doronicum, Senecio, 
Telekia, Buphthalmum, Anthemis, Matricaria, and others) the branches of the stigmas 
curve back like a bow, so that the pollen clinging to the hairs. of the style reaches 
the stigmatic surfaces of the older adjacent florets. This is rendered particularly 
easy in these flowers by the fact that the torus is arched, so that the inner and 
younger florets (which are covered with pollen) are necessarily at a higher level than 
the outer and older ones, which are already in the female condition. 
Among Umbelliferae the arrangements leading to Geitonogamy are scarcely 
less varied than in Compositae. Kerner (op. cit., pp. 323-5) describes the arrange- 
ments in question present in Eryngium, Astrantia, Sanicula, Laserpitium, Pachy- 
pleurum, Siler, Athamantha, Meum, Chaerophyllum (see Fig. 2), Anthriscus, 
Foeniculum, Coriandrum, Sium, Ferulago. Kerner further mentions that these may 
serve as types for numerous plants of other families, of which the flowers are 
crowded together in heads, clusters, corymbs, spikes, or racemes; especially among 
the Cornaceae, Caprifoliaceae, Rubiaceae, Scrophulariaceae, Rosaceae, Polygonaceae, 
Liliaceae, Aroideae. He subsequently describes the Geitonogamy of Calla palustris, 
Saxifraga juniperifolia; Veronica maritima, spicata, and spuria ; Eremurus caucasicus, 
Allium victorialis, Polygonum Bistorta, Rheum, Rumex alpinus; Thalictrum alpinum, 
foetidum, and minus; Erica carnea, Lathraea squamaria, Clandestina rectiflora, 
Bartsia alpina, Crucianella stylosa. These relations are briefly described in the 
second volume of my work in dealing with floral adaptations, so far as the plants 
named by Kerner belong to the European Flora. 
IV. Xenogamy. 
Reference has already been made in the historical part to the significance of 
Xenogamy, which was first recognized by Darwin, as well as to the modification 
by Hermann Miiller of the resultant Knight-Darwin law. It occurs not only among 
diclinous plants, but also in most monoclinous plants, since, in the latter, male 
and female floral stages are brought about by Dichogamy. As already mentioned 
in the synopsis of floral arrangements (p. 29) only cross-pollination is possible 
in such cases, for as stamens and carpels mature at different times, the stigmas have 
shrivelled up by the time the anthers dehisce, or vice versa. In plants where 
Dichogamy is not so well marked cross-pollination predominates at first, but self- 
pollination later on becomes possible. 
