REMOVAL OF POLLEN IN ORCHIDS. 



255 



is licked up by small beetles. In other instances the back of the lip is produced 

 into a spur lined with cells full of sweet juice, to which insects obtain access by 

 piercing the walls of the cells. The genus Orchis affords an example of this. 

 Honey of a sort peculiarly attractive to butterflies is secreted in the tubular spur 

 in other cases, such as Gyrimadenia and Habenaria (see fig. 258 ^, p. 227). 



Two separate particles of viscid matter are often produced on the rostellum, 

 each being in connection with one only of the pollen-masses (e.g. Habenaria 



Fig. 268. — Withdrawal and deposition of pollinia in the flowers of an Orchid 



Flowering spike of the Broad-leaved Helleborine (Epipactis latifolia) upon which a wasp (Vespa Austriaca) is alighting. 

 ^ A flower of the same seen from the front. » Side view of the same flower with the half of the perianth towards the 

 observer cut away. * The two pollinia joined by the sticky rostellum. s The same flower being visited by a wasp, which 

 is licking honey and at the same time detaching witli its forehead the tip of the rostellum together with the pair of 

 pollinia. e The wasp leaving the flower with the pollinia cemented to its head ; the pollinia are erect. ? The wasp 

 visiting another flower and pressing its forehead with the pollinia (which in the meantime have bent down) against the 

 stigma. 1 nat. size ; the other figures x 2. 



chlorantha, the Large Butterfly Orchis). Insects then frequently only draw one 

 of the pollen-masses out of the anther, instead of both, as they leave the flower. 

 In species of the Twayblade genus (Listera) the rostellum is scale-like and 

 arches over the stigmatic surface. At the commencement of the flowering 

 period it is not connected with the pollinia, but the moment it is touched it 

 exudes a drop of viscid fluid which sticks, on the one hand, to the body touching 



