PHENOMENA OF EEPEODUCTION. 155 



hours he found the latter discoloured, withered, and deeply penetrated by a number 

 of pollen-tubes ; he then made the reverse experiment on a long-styled flower, and 

 this heteromorphic fertilization had the same result as the first. Lastly, he placed 

 the pollen of a long-styled flower on the stigmas of a similar flower, but belonging 

 to another plant ; but at the end of three days not a single pollen-grain had emitted 

 a tube. In another experiment, Mr. Darwin placed on three of the stigmas of a 

 long-styled flower pollen belonging to the same type, and on the two others pollen 

 from a short-styled flower. At the end of twenty-two hours these two stigmas 

 were discoloured and penetrated by numerous pollen-tubes ; the three other stigmas 

 covered with pollen of their own type remained fresh, and the pollen-grains scarcely 

 adhered to them. In TAnum perenne, dimorphism is even more obvious that in 

 L. grandiflorum ; the pistil of the one form is much longer, and the stamens much 

 shorter than in the other. Mr. Darwin has ascertained, by numerous experiments 

 on each of the two forms, that the stigmas of one can be impregnated only by pollen 

 from the stamens of the other. 



It is hence absolutely necessary that insects should carry the pollen from the 

 flowers of one form of Linum to those of the other ; and to these they are attracted 

 by five minute drops of nectar secreted on the exterior of the base of the stamens : 

 to reach these drops, the insect is obliged to insert its trunk between the staminal 

 whorl and the petals. Now, in the short-styled form, if the stigmas, which were 

 originally vertical and faced the floral axis, had preserved this position, their backs 

 only would have been presented to the insect, and the flower could never be thus 

 fertilized ; but the styles having diverged, and protruding between the filaments, the 

 stigmatic surfaces are turned upwards, and rubbed by every insect which enters the 

 flower, thus receiving the pollen which fertilizes them. 



In the long-styled form of L. grandiflorum the styles diverge very slightly, and 

 the stigmas project a little above the corolla-tube, so as directly to overhang the 

 passage leading to the drops of nectar ; consequently, after an insect has visited the 

 flowers of either form, it withdraws its trunk well covered with pollen. If it then 

 plunges its trunk into a long-styled flower, it necessarily leaves some of this pollen 

 on the papillse of the stigmas ; if it plunders a short-styled flower, it still deposits 

 pollen on its stigmas, the papillae of which are here turned upwards. Thus the 

 stigmas of the two forms receive indifferently the pollen of both, though fertilization 

 of each can only be effecited by the pollen of the opposite form. 



In the long-styled type of L. perenne the styles do not sensibly diverge, but they 

 twist so as to reverse the position of the stigmas, whence the inner surfaces are 

 turned outwards ; thus an insect seeking nectar in the flower brushes against the 

 stigmatic surfaces, and leaves on them the pollen collected from another flower. 



The facts here recorded demonstrate both the object of dimorphism, and the im- 

 portant part which insects play in the fertilization of plants. Mr. Darwin complains 

 that certain botanists attribute the transport of pollen to the wind and insects indif- 

 ferently, as if there were no important difference between the action of these two 

 agents. Dioecious plants, or even hermaphrodite ones, in the fertilization of which 

 the wind is a necessary auxiliary, present peculiarities of structure fitted for this 



