How the Sweet-pea protects its Seed-vessel 2 1 1 



them are concealed the pistil and the stamens. From their 

 curved shape they are named "the keel." It is only faintly 

 coloured, and is open by a slit in its upper edge, but usually 

 closed below. At its very end the projecting tip of the pistil 

 (the stigma) may probably be seen. Carefully tear off and 

 remove the petal portions of this keel. You will disclose an 

 inch-long slender bar, glistening and greyish-white on its sur- 

 face, and ending in front by a circlet or collar formed by the 

 anthers of a number of stamens, from the midst of which the 

 pistil, as we have already seen, conspicuously projects. The 

 greyish-white surface just mentioned is a delicate tissue- 

 paper-like membrane, made up of the filaments of these 

 stamens, which have joined together at their sides (become 

 coherent), and constitute a sheath for the seed-vessel within, 

 which latter gives solidity to the whole structure. From this 

 examination of the flower and the young seed-vessel turn 

 now to a well-grown pod. This is shaped like a straight- 

 backed knife, with a sort of join (a suture) above and below, 

 and a little eighth of an inch bowsprit or flagstaff at its 

 extremity. Along its upper or straight suture, which, by the 

 way, is the thickest one, you will easily detect a row of seeds. 

 There are none along the lower edge. The pod has now no 

 sheath, and it is green, not grey. If we look, however, at its 

 base, close within the green leaves which are the remains of 

 the calyx, and just under the lower edge of the pod, you will 

 find a short bit of ribbed satiny membrane fringed at its front 

 edge and firmly attached behind. This structure is what 

 remains of the delicate tube which in an earlier stage en- 

 sheathed the whole pod. The sheath has been torn open by 

 the force of the onward-growing and swelling pod, and it has 

 given way by a long slit of its upper surface. If we look a 

 little closer we shall see that this slitting by distension has 

 not occurred at random, but that arrangements were made 

 for it beforehand. It is not a single tear, as at first sight it 

 looked, nor has it occurred exactly in the middle line. A 

 single stamen has been left solitary on the upper surface, the 



