DARWIN. 105 



many cases the pollen masses slowly change their position 

 while adhering to the insects, and so assume a proper 

 direction for striking the stigma of another flower, and 

 the insects during this interval will almost certainly have 

 flown from one plant to another. 



The family to which Catasetum belongs furnished the 

 rnost remarkable examples. This plant possesses a 

 special sensitiveness in certain parts, and when definite 

 points of the flower are touched by an insect the pollen 

 masses are shot forth like an arrow, the point being blunt 

 and adhesive. The insect, disturbed by so sharp a blow, 

 or having eaten its fill, flies sooner or later to a female 

 plant, and whilst standing in the same position as before, 

 the pollen-bearing end of the arrow is inserted into the 

 stigmatic cavity, and a mass of pollen is left on its viscid 

 surface. The strange structures of Cypripedium, or the 

 Lady's Slipper, were then analysed, and the mode of fer- 

 tilisation by small bees was discovered. The whole 

 structure of orchids, as modified to secure insects' visits 

 and cross fertilisation, was now expounded, and the 

 benefits shown by cases where insects' visits were pre- 

 vented, and no seed was set. The number of seeds in a 

 capsule was reckoned, and thence it was found that the 

 progeny of a single plant of the common orchis would 

 suffice to cover the globe in the fourth generation. A 

 single plant of another orchid might bear seventy-four 

 millions of seeds : surely an ample provision for a 

 struggle for existence, and selection and survival of the 

 fittest. But, as Darwin remarks, profuse expenditure is 

 nothing unusual in nature, and it appears to be more 

 profitable for a plant to yield a few cross-fertilised than 

 many self-fertilised seeds. 



