Chap. IV. LISTEEA OVATA. 121 



and to the tips of the poUinia. The insect was not 

 so large as one of the pollinia, and after causing the 

 explosion had not strength enough to remove them ; 

 it was thus punished for attempting a work beyond 

 its strength, and perished miserably. 



In Spiranthes the young flowers, which have their 

 pollinia in the best state for removal, cannot possibly 

 be fertilised ; they must remain in a virgin condition 

 until they are a little older and the column has 

 moved away from the labellum. Here the same end 

 is gained by widely different means. The stigmas of 

 the older flowers are more adhesive than those of the 

 younger flowers. These latter have their pollinia 

 ready for removal ; but immediately after the rostellum 

 has exploded, it curls forwards and downwards, thus 

 protecting the stigma for a time; but it slowly be- 

 comes straight again, and now the mature stigma is 

 left freely exposed, ready to be fertilised. 



I wished to know whether the rostellum would 

 explode, if never touched ; but I have found it difficult 

 to ascertain this point, as the flowers are highly at- 

 tractive to insects, and it is scarcely possible to exclude 

 very minute ones, the touch of which suffices to cause 

 the explosion. Several plants were covered by a net 

 and left till the surrounding plants had set their 

 capsules ; and the rostella in most of the covered-up 

 flowers were found not to have exploded, though their 

 stigmas were withered, and the pollen mouldy and 

 incapable of removal. Some few of the very old 

 flowers, however, when roughly touched, were still 

 capable of a feeble explosion. Other flowers under 

 the nets had exploded, and they had the tips of their 

 pollinia fixed to the crest of the rostellum ; but whether 

 these had been touched by some minute insect, or had 

 exploded spontaneously, it was impossible to deter- 



