PART ILI. | THE MECHANISMS OF FLOWERS. 419 
enough for large humble-bees to insert easily the head and part of 
the thorax, and smaller humble-bees more than half of their body ; 
while still smaller bees can enter the tube bodily. The insect 
passes straight on to the base of the flower, the downward curva- 
_ ture of whose terminal portion corresponds to that of the insect’s 
proboscis, To alight on the flower and suck the honey is the work 
of a moment; so completely is the shape of the flower adapted, 
not for one only, but for many species of bees, But none of the 
various visitors can reach the honey without getting dusted ven- 
trally with pollen in young flowers, or leaving some of that pollen 
upon the stigma in older flowers, From the point where the 
filaments become free from the corolla, they pass on horizontally’ 
near the inferior wall of the corolla; and the four lowest stamens 
project some 7 mm. beyond the corolla, forming a convenient 
_ alighting-place for insects. The uppermost stamen, on leaving its 
_ attachment to-the corolla, also bends downwards, and in so doing 
it divides the entrance to the honey-containing part of the tube 
_ into two passages ; it then proceeds horizontally, but only so far as 
the mouth of the corolla. The free ends of all the stamens curve 
slightly upwards; and the anthers, which dehisce as the flower 
. opens, turn their pollen-covered sides upwards ; no bee, therefore, 
can alight without dusting its ventral surface with pollen. Large 
' humble-bees bring their thorax, smaller ones their abdomen, in 
contact with the long stamens, while the smallest bees, which fly 
| right into the flower, must at least come in contact ventrally with — 
| the short fifth stamen. The style lies in the midst of the stamens, 
and divides terminally into two short branches, which bear the 
stigmas at their ends. When the flower opens, the style scarcely 
' reaches the mouth of the corolla; its distal end is straight, its two 
branches lie close together, and their stigmas are apparently in- 
capable of fertilisation. In course of time the style lengthens till 
| it projects 10 mm. beyond the mouth of the corolla; it curves 
' gently upwards at its outer end, and its two branches, now 
| bearing ripe stigmas, separate. The stigmas now lie above 
} and in front of all the anthers, and no bee, large or small, can 
/ enter the flower without bringing its ventral surface in contact 
: with them. 
| It is evident from the position of the stigmas that cross- 
| fertilisation will be performed, even if pollen remains upon the 
| anthers when the stigmas are mature. 
i Echium attracts very numerous and various insects, as the 
| following long list shows :-— 
| EE 2 
