Feriilisation of Scrophularia aquatica and S. nodosa. 385 



Now it might be supposed that the peculiar features 

 presented by the inflorescence and flowers of these plants 

 were wholly due to the selective influence of wasps, but a 

 careful study of the habit and action of bees on S. aquatica 

 points to the conclusion that modification has gone on in 

 two difl'erent directions, viz., first and chiefly, in adaptation 

 to wasps in order to ensure the maximum amount of cross- 

 fertilisation ; secondly, for the purpose of rendering the 

 plants unattractive to bees. 



In regard to the former case, it may be briefly said that 

 the plants show adaptation to wasps in tlie general struc- 

 ture, disposition, and relation of the flowers ; in the close 

 proximity of difl'erent racemes, so that many of the flowers 

 of one are intermingled with those of others, the wasps 

 being thus lured from one raceme to another; and in the 

 duration of the period of flowering, which begins when 

 wasps become abundant, and terminates almost to a day 

 with the disappearance of these insects. In November 

 the last wasps of the year may be found, chilled and 

 torpid, clinging to the leaves or flowers, which simultan- 

 eously have the movements of their reproductive organs 

 arrested : that degree of cold inimical to the one destroys 

 the other. 



There are several minor advantages to the plant from 

 having wasps instead of bees as the agents of fertilisation : 

 they work later in the day, later in the year, and in windy 

 weather when no bees are on the wing; their carnivorous 

 habits secure immunity from the visits of merely pilfering 

 insects, and, above all, because there are exceedingly few, 

 and in some districts no other floral competitors for their 

 visits. 



In regard to the second point, that bees are really 

 injurious is highly probable from tlie following considera- 

 tions:—!. They often ingeniously thrust their proboscis 

 into scarcely opened flowers, and steal the nectar before the 

 stigma is mature. 2. Even when the developed stigma is 

 in a position to be fertilised, their slender proboscis can 

 reach the nectar by the side of the upcurved style without 

 the stigma being touched. 3. Many, but not all, of the 

 humble-bees can always reach the nectar without neces- 

 sarily touching the reproductive organs. 4. From their 



