AND INSECT xVID. 231 



as heteromorphous ; those which have two forms of flower, hke 

 the primrose, as dimorphous ; and those which have three forms, 

 as in Lythriun salicaria (Purple Loosestrife), as trimorphous. 

 Sprengel, as Darwin mentions, had noticed this difference in form 

 \\\ Hotfonia before 1793. " Sprengel," writes Darwin, " with his 

 usual sagacity, adds that he does not believe the existence of the 

 two forms to be accidental, though we cannot explain their purpose." 

 Trimorphism was noticed by A^aucher in 1841, and by \\ irtgen in 

 1848. It was left to our great naturalist, Charles Darwin, to 

 interpret, in the Journal of the Linnrean Society, 1862, this curious 

 phenomenon. 



Referring to dimorphism in the case of the primrose. Sir John 

 Lubbock observes, "An insect thrusting its proboscis down a 

 primrose of the long-styled form, would dust its proboscis at a 

 part which, when it visited a short-styled flower, would come just 

 opposite the head of tlie pistil, and could not fail to deposit some 

 of the pollen on the sligma. Conversely, an insect visiting a short- 

 styled plant would dust its proboscis at a })art further from the top ; 

 which when the insect consequently visited a long-styled flower 

 would again just come opposite the head of the pistil. Hence we 

 see that by this beautiful arrangement insects must carry the pollen 

 of the long-styled form to the short-styled, and vice versa." Mr. 

 Darwin has shown that much more seed is set, if pollen from the 

 one form be placed on the pistil of the other, than if the flower 

 be fertilised by pollen of the same form, even taken from a 

 different plant. 



This eminent naturalist, in his interesting work on the forms 

 of flowers, after giving a minute and graphic description of trimor- 

 phism in the case of Ly thrum saiicaria (Purple Loosestrife), 

 observes, " In a state of nature the flowers are incessantly visited 

 for their nectar by hive or other bees, various Diptera, and Lepi- 

 doptera. The nectar is secreted all round the base of the 

 ovarium ; but a passage is formed along the upper and inner side 

 of the flower by the lateral deflection of the basal portion of the 

 filaments ; so that insects invariably alight on the projecting 

 stamens and pistils, and insert the proboscis along the upper and 

 inner margin of the corolla. \Yo can now see why the ends of 

 the stamens with their anthers, and the end of the pistil with the 



