i.] SCROPHULARIA. 17 



or less dependent on insects, from G.pratense to which 

 they are necessary, to G. pusillum, which is quite 

 independent of them ; while the size of the corolla 

 increases with the dependence on insects. 



In those species in which self-fertilisation is pre- 

 vented by the circumstance that the stamens and 

 pistil do not come to maturity at the same time, the 

 stamens generally ripen first. 



The advantage of this is probably connected with 

 the visits of bees. In those flowers which grow in 

 bunches the lower ones naturally open first. Con- 

 sequently in any given spike the flowers are at first all 

 male ; subsequently the lower ones, being the older, 

 have arrived at the female stage, while the upper ones 

 are still male. Now it is the habit of bees to begin 

 with the lower flowers of a spike and work upwards. 

 A bee, therefore, which has already dusted herself with 

 pollen from another flower, first comes in contact with 

 the female flowers, and dusts them with pollen, after 

 which she receives a fresh supply from the upper male 

 flowers, with which she flies to another plant. 



There are, however, some few species in which the 

 pistil ripens before the stamens. One is our common 

 Scrophularia nodosa. Now why is this ? Mr. Wilson 

 has given us the answer. .S. nodosa is one of our few 

 flowers specially visited by wasps ; the honey being 

 not pleasing to bees. Wasps, however, unlike bees, 

 generally begin with the upper flowers and pass down- 

 wards, and consequently in wasp flowers it is an ad- 

 vantage that the pistil should ripen before the stamens. 

 But though the stamens generally ripen before the 

 pistil, the reverse sometimes occurs. Of this a very 



