166 Fertilization of Flowers. 



length the progeny from seeds thus produced is nearly always weak or 

 sterile, thus showing that the fertilization was illegitimate and not for 

 the good of the species. 



Not only floral structure, but also floral arrangement combined with 

 successive expansion of flowers are found to be conducive to cross- 

 fertilization. 



Many plants have their flowers in elongated clusters, spikes or 

 racemes, the single flowers being generally small and opening succes- 

 sively from the base toward the apex of the cluster. Moreover, they 

 generally mature their pollen before the stigmas are receptive. If now 

 a bee or other insect visits the raceme of a cardinal flower or a door- 

 yard plantain when the flowers have just begun to open, it finds the 

 pollen in good condition but the stigmas of such flowers are not yet 

 receptive. Its body becomes dusted with the pollen but it must fly to 

 another earlier flowering plant to deposit it on the stigmas. If the 

 raceme has been in blossom sometime, the lower flowers have their 

 stigmas receptive and their stamens withered, while the upper flowers 

 have their stamens in good condition but their stigmas not yet recep- 

 tive. Bees usually settle on the lower flowers first and work upward, 

 thus passing from the uppermost flowers of one raceme to the lower of 

 another, a practice favorable to cross-fertilization. They likewise 

 manifest a good knowledge of species. Having commenced working 

 on a certain kind of flower they do not like to leave it for some other. 

 They are not given to mixing honey or pollen of different kinds 

 together. But should pollen by any chance be brought from one kind 

 of flower to the stigmas of another species it is not likely to do any 

 harm. The probabilities are entirely against its germination in such 

 a foreign position. Nature appears to have placed two limitations on 

 this process. She manifests her displeasure with too close fertilization 

 and with too distant fertilization. As a rule she forbids a union 

 between the essential organs of the same flower on one hand and of 

 flowers of different species on the other. She would avoid incestuous 

 deterioration as well as inextricable confusion and hybridization. 



It might here be stated that certain floral structures favor the visits 

 of certain insects to the exclusion of others. Ants are fond of honey 

 but they are generally wingless and consequently are poor pollen 

 carriers. Many plants, therefore, present obstacles to their visits. In 

 some, like the shooting star, Dodecatheo?i Meadia, the calyx is strongly 

 reflexed, in others it is bristly with rigid setae, or clothed with viscid 

 glandular hairs. In others still, as in some of the catch flies the 

 internodes of the stem are girt by a glutinous band, which serves to 



