862 ECOLOGY 



there being some varieties which mature edible fruits (though without viable seeds) 

 without caprification or pollination. Other varieties, notably the Smyrna &g, re- 

 quire pollination for their best' development, the caprified fruits surpassing those 

 that are not caprified in plumpness, juiciness, and flavor. 



Geitonogamy. — General remarks. — In spite of the numerous and 

 remarkable features which facilitate cross pollination, geitonogamy (or 

 pollination between different flowers of the same plant) and close polli- 

 nation are very common and, taken together, perhaps are more common 

 in monoclinous flowers than is cross pollination. Furthermore, there are 

 cases in which the features facilitating these kinds of pollination are about 

 as specialized as any that have been previously noted in connection with 

 cross pollination. In most species a number of flowers bloom at once on 

 the same plant, so that dichogamy does not prevent geitonogamy, es- 

 pecially because insects usually visit all the flowers on a given plant before 

 flying to another. The first flower on each plant visited may get only 

 foreign pollen, but the chance of geitonogamy increases with the number 

 of flowers visited, though it should be remembered that the general 

 prepotency of foreign pollen greatly favors the latter in initiating seed 

 production. Geitonogamy is commonest in plants with compact in- 

 florescences, especially where these are umbels, spikes, or heads, as in 

 the umbellifers (the highest of the polypetalous dicotyls) and in the 

 composites (the highest of plants). While such floral massing does not 

 exclude cross pollination, it so greatly facilitates geitonogamy that the 

 latter probably is the chief method of pollination. Although the almost 

 habitual dichogamy of these plants prevents autogamy and peculiarly 

 facilitates geitonogamy, there is no adequate evidence that the latter is 

 perceptibly more advantageous than the former. 



Illustrations of geitonogamy in the composites and umbellifers. — The culmination 

 of conditions favorable to geitonogamy occurs in the composites, a group that is 

 notably protandrous. The outer flowers bloom first, but the stigmas remain recep- 

 tive until the flowers next within shed pollen. After the stamens mature, the style 

 elongates, pushing up through the surrounding tube of united anthers and swabbing 

 out some of the pollen, which adheres to the style bristles. Later the style forks, 

 exposing the receptive stigmatic surfaces (fig. 1182), which with the adherent 

 pollen commonly come into contact with the stigmatic surfaces of adjoining 

 flowers. Entangled style branches of this sort are especially conspicuous in Eupa- 

 iorium. In contrast to pollination by wind or insects, this may be termed contact 

 pollination. Geitonogamy by contact is especially characteristic of the milky- 

 juiced composites (such as the dandelion, figs. 1193, 1194), since the heads open by 

 day and close at night and in rainy weather, insuring to an unusual degree the 

 contact of stigmas and pollen-covered organs of adjoining flowers. 



