32 



31 distinct visitors upon tlie purple colored ffowers of Malva 

 sylvest is AuA on\y iour on the small white flowered Malva 

 rotund (folia, Heracleum spondylium 118, Aegapodium podagra- 

 aria 104, Anthriseus sylvestris 73, Daucuscarota 61, Cnicus ar- 

 vensis 88, Centaureajacea 4:8, Tanacetum vulgare 28. He says 

 although it is impossible in statistical tables to take into ac- 

 count the various conditions which may modify the visits of 

 insects, the general law holds good that the more conspicuous 

 flowers are visited more frequently than others. 



Mr. Robertson well shows that: "Concealment of nec- 

 tar, however, accomplishes one important result that cannot 

 be accomplished by a change in time of blooming, and that 

 is the simultaneous exclusion of flies and short-tongued hym- 

 enoptera. The effect of concealment of neetar can only be 

 ascertained by comparison with a form having free honey, 

 and blooming at the same time with Eryngium and Cicuta." 



The first condition which seems to be a departure from 

 the original type readily to induce departures of a more seri- 

 ous nature is an aggregation of flowers in a more or less 

 close cluster. In this case the lower lip loses its distinctive 

 function both as a vexillary organ and as a landing place. 

 Both ofBces are immediately assumed by the inflorescence 

 itself. VAs long as the flowers remain separate, they attract 

 the insects which are pleased by the special floral form and 

 are adapted to it. But when the flowers become clustered 

 they attract less specialized insects to what appears an undif- 

 ferentiated color mass. In a similar way, separated flowers 

 are only readily visited by insects to which the lower lip 

 forms a convenient resting place. But when the flowers 

 form a compact inflorescence, a landing place is formed by 

 the flower cluster. Even when the floral Structure remains 



