122 NEOTTE^. Chap. IV, 



mine. It should be observed, that although I looked 

 carefully, not a grain of pollen could be found on the 

 stigmas of any of these flowers, and their ovaria had 

 not swollen. During a subsequent year,, several plants 

 were again covered by a net, and I found that the 

 rostellum lost its power of explosion in about four 

 days ; the viscid matter having turned brown within 

 the loculi of the rostellum. The weather at the time 

 was unusually hot, and this probably hastened the 

 process. After the four days the pollen had become 

 very incoherent, and some had fallen on the tv/o 

 corners, and even over the whole surface of the stigma, 

 which was penetrated by the pollen-tubes. But the 

 scattering of the pollen was largely aided by, and 

 perhaps wholly depended on, the presence of Thrips 

 — insects so minute that they could not be excluded 

 by any net, and which abounded on the flowers. This 

 plant, therefore, is capable of occasional self-fertilisa- 

 tion, if the access of winged insects be prevented ; but 

 I have every reason to believe that this occurs very 

 rarely in a state of nature. 



That insects do their work of cross-fertilisation 

 effectually is shown by the following cases. The 

 seven upper flowers on a young spike with many 

 unexpanded buds, still retained their pollinia, but 

 these had been removed from the ten lower flowers ; 

 and there was pollen on the stigmas of six of them. 

 In two spikes taken together, the twenty-seven lower 

 flowers all had their pollinia removed, and had pollen 

 on their stigmas; these were succeeded by five open 

 flowers with the pollinia not removed and without any 

 pollen on the stigmas ; and these were succeeded by 

 eighteen buds. Lastly, in an older spike with forty- 

 four fully expanded flowers, the pollinia had been 

 removed from every single one ; and there was pollen, 



