Fertilisation 0/ Scropbularia aquatica and S. nodosa. 387 



tilised flowers, and although not uncommon in those 

 fertilised by Hies, it is one of the least attractive to bees, 

 and is, besides, in itself very inconspicuous. I was espe- 

 cially impressed by this when using gauze nets to envelop 

 portions of the raceme for experimental purposes. I 

 first used dark green, but found that brown coloured ones 

 were much less noticeable. Wlien the flowers become 

 blanched to a light green tint, as they ultimately do when 

 cut racemes are kept standing in water in a shady room, 

 they are more conspicuous at a distance than are the 

 brownish-purple ones. It seems probable, therefore, that 

 the colour is really protective. In reference to this point 

 it is a noteworthy fact that the ripening ovary develops a 

 dark purplish hue ; and since it is clasped by the persistent 

 and relatively large calyx (whose tension previously 

 squeezes off" the loosened corolla) it simulates to some 

 degree the perfect flower. The buds, too, so different in this 

 respect from those of the majority of plants, are as deeply 

 coloured as the opened flowers. The object of these appa- 

 rently unimportant features may therefore be to shield the 

 flowers by simulating them, and the result is apparent in 

 the close scrutiny made by the insects up and down the 

 racemes. On one occasion I observed a wasp carefully 

 searching a brown seeding dock that grew on the edge of a 

 clump of S. aquatica, apparently mistaking it for the 

 inflorescence of the latter, and I have frequently seen 

 them on the point of alighting on buds and maturing 

 ovaries. 



But probably more important is the wide dispersion of 

 the flowers. Aggregation is one of the most potent of 

 the subsidiary attractions for bees, as enabling them to 

 obtain the maximum of honey or pollen in the minimum 

 of time. For instance, the individual flowers of Eeseda 

 liiteola are small, colourless, inconspicuous, and odourless ; 

 yet there are few inflorescences more thronged with bees. 

 The complete concealment of the honey in a valvular 

 chamber to which the bee alone has the key, doubtless has 

 something to do with this partiality ; but the very close 

 aggregation of the flowers furnishes a strong inducement, 

 as there are more flowers on one inch of its raceme than 

 on the whole inflorescence of S. aquatica. 



