126 KEOTTEiE. CHiP. IV. 



sion caused, the pollen-masses are not so neatly caught 

 by their tips as those of Listera. Thus a good deal of 

 the friable pollen is often left behind in the anther- 

 cells and is apparently wasted. Several plants were 

 protected from the access of winged insects by a net, 

 and after four days the rostella had almost lest their 

 sensitiveness and power to explode. The pollen had 

 become extremely incoherent, and in all the flowers 

 much had fallen on the stigmas which were penetrated 

 by the pollen-tubes. The spreading of the pollen 

 seems to be in part caused by the presence of Thrips, 

 many of which minute insects were crawling about the 

 flowers, dusted all over with pollen. The covered-up 

 plants produced plenty of capsules, but many of these 

 were much smaller and contained fewer seeds than 

 those produced by the adjoining uncovered plants. 



If insects had been forced by the labellum being 

 more upturned to brush against the anther and stigma, 

 they would always have been smeared with the pollen 

 as soon as it became friable; and they would thus 

 have fertilised the flowers effectually without the aid 

 of the explosive rostellum. This conclusion interested 

 me, because, when previously examining Cephalan- 

 thera, with its aborted rostellum, its upturned label- 

 lum and friable pollen, I had speculated how a transi- 

 tion, with each gradation useful to the plant, could 

 have been effected from the state of the pollen in the 

 similarly constructed flowers of Epipactis, with their 

 pollinia attached to a well-developed rostellum, to the 

 present condition of Cephalanthera. Neottia nidus- 

 avis shows us how such a transition might have been 

 eflected. This Orchid is at present mainly fertilised 

 by means of the explosive rostellum, which acts effec- 

 tually only as long as the pollen remains in mass; 

 but we haye seen that as the flower grows old the 

 pollen swells and becomes friable, and is (hen apt to 



