PART Int | THE MECHANISMS OF FLOWERS. 91 
the angles between stamens and ovary, which are always found to 
be quite full of honey. Every insect-visitor must thrust its 
_ proboscis into one of these angles; and in doing so it causes the 
two stamens which the base of its proboscis touches to spring 
inwards towards the pistil, and to dust with pollen one side of its 
head, which is thus shut in between two anthers and the stigma. 
The stigma is. represented by the papillose and viscid edge of a 
dise which surmounts the ovary and occupies the middle of the 
flower ; one side of the insect’s head, opposite to that touched by 
the stamen, comes in contact with the stigma. The insect usually 
flies away at once after the first drop of honey on being struck by 
_ the stamen, and as it thrusts its head or proboscis into the flower 
in many different ways as the different positions of the flower 
“a 
Fia. 30.— Berberis vulgaris, L. 
1 
a 
. 1.—Flower seen from above. a, the three inner. larger sepals, which by their size and colour play 
_ the part of a corolla; 6b, outer, b’, inner petals, ; ¢, nectaries; d, filaments ; e, stigma, 
ig 2.—Position of the stamen after springing inwards. 
8.— Petal with its two thick fleshy, orange nectaries. 
4—7.—Stamens in various stages of dehiscence, erection, and rotation of the anther-valves. 4, 
_ stamen with the anther-valves still closed ; 5, the valve of the right anther-lobe has opened, and is 
beginning to move upwards, with the pollen attached to it; 6, both valves have nearly completed 
_ their movement of rotation, the pollen masses are directed towards the right and left ; 7, both valves 
_ have turned in such a way that the pollen-masses face the centre of the flower, and touch one 
another with their adjacent edges ; 7b, ditto, inner aspect. 
_ require, now under now over the stigma, now to the right, now to 
the left, its head must soon be dusted all round with pollen, and it 
| must fertilise every succeeding flower that it visits, It can only 
| _ accomplish self-fertilisation if in the same flower it plunges its 
| proboscis first to the right and then to the left, or first over and 
if then under the stigma. In the case of the hive-bee I have 
Bpeistinctly observed that it seldom proceeds in this manner, It 
never makes a circuit of the flower, for it flies away and seeks 
