26 TRANSFERENCE OF POLLEN. [chap. 



to be the case in Corydalis cava and Pulmonaria 

 (Fig. 96), by Gartner in Verbascum nigrum (Fig. 98), 

 and Lobelia fulgens ; by Scott in Primula verticillata, 

 Uncidium, &c. 



Other cases are recorded in which plants are more 

 or less insusceptible of fertilization by their own 

 pollen. Moreover, even where plants are capable of 

 self-fertilization, the pollen from another flower is 

 often more effective than their own, whence it fol- 

 lows that if a supply of pollen from another plant 

 be secured, it is comparatively unimportant to ex- 

 clude the pollen of the plant itself; for in such cases 

 the latter is neutralized by the more powerful effect of 

 the former. 



Everyone who has watched flowers, and has ob- 

 served how assiduously they are visited by insects, 

 will admit that these insects must often deposit 

 on the stigma pollen brought from other plants, 

 generally those of the same species ; for it is a re- 

 markable fact that in most cases bees confine them- 

 selves in each journey to a single species of plant; 

 though in the case of some very nearly allied forms 

 this is not so ; for instance, it is stated, on good 

 authority, that Ranunculus acris, R. repens, and R. 

 bulbosus, are not distinguished by the bees, or at 

 least are visited indifferently by them, as is also the 

 case with two of the species of clover, Trifolium 

 fragiferum and T. repens. 



Even in the simplest and most regular flowers, 

 where the stamens surround the pistil, and both are 

 mature at the same time, insects may visit the flower, 

 and yet not fertilise it with its own' pollen, because 



