INSECT POLLINATION 321 



nature of these flowers will be found in the study of the 

 Early Purple Orchis (Orchis tnascula, Plate LXIV.) • The 

 flowers are arranged in a spike, each one being attached 

 to the stalk by the base of its twisted ovary, and having 

 a long spur in which honey is secreted. One petal, 

 which is three-lobed, forms a landing-stage for insects, 

 while the remaining two petals form a hood protecting 

 a pair of pollen-sacs, which do not appear conspicuously 

 like ordinary stamens. At the point of attachment of 

 the perianth to the ovary there is a stigmatic surface. 

 If we push a pencil- point foremost into the mouth of a 

 flower which has not already been visited by an insect, 

 the pencil will come into contact with an adhesive disc 

 at the base of the pollen-sacs, and when it is withdrawn 

 one or both of these masses, called the 'pollinia, will be 

 found adhering by the disc to the pencil. At first the 

 pollinia are nearly upright, but in a few seconds they 

 bend over and forward until they are about horizontal. 

 This little experiment illustrates what happens when 

 an insect, say a bee, visits Orchis mascula in order to get 

 honey. It alights on the landing-stage, pushes forward 

 into the mouth of the flower, and, extending its tongue, 

 sips at the nectareous fluid in the spur. While it is 

 thus engaged the pollen-masses have been liberated, and 

 have attached themselves by their sticky disc on the 

 head of the insect, probably on one of its eyes. The 

 bee leaves the flower with the pollinia attached to its 

 head, and as it proceeds rapidly to another flower for 

 more honey, the pollinia bend forward, as on the pencil. 

 In entering the next flower, the bee, in its haste for 

 honey, is compelled to push the pollen-mass against the 

 stigmatic surface, and thus cross-fertilization ensues. 



4X 



