2IO 



The Museum Gazette 



the placenta and the seeds. The curve may vary, and some- 

 times neither border seems more curved than its fellow. In 

 all cases we must note which suture looks the thickest, for 

 that will be one which bears the seeds. It is the thickest 

 and strongest, because it is the one which is backed up by 

 the placenta, and the other being the weaker is the one to 

 give way first. Every one who has shelled peas knows that 

 when the pod has been made to split the peas remain in line 

 along the bottom of the opened pod. From this position it 

 is usual to dislodge them by the back of the thumb-nail. 



In order to realise that the pod is, in embryo, constructed 

 by the folding of a leaf, take any long oval leaf and place its 

 free borders together. It may seem curious that this joining 

 of the edges (or suture) should become the strongest part, for 

 it would seem more likely that the midrib would be so. It 

 is, as we have said, the subsequent growth of the placenta 

 which strengthens it. It is not very difficult to assign a 

 reason for the growth of the placenta and seeds at this suture, 

 rather than at the other, for the free borders of leaves are 

 their growing parts, and much more prone to new develop- 

 ments than the central midrib, which is a fixture. 



HOW THE SWEET-PEA PROTECTS ITS 

 SEED-VESSEL. 



Before the last sweet-pea of the season has withered, let 

 us go and gather it, and together with it get some seed-pods 

 in different stages of their growth. We shall find them 

 well worthy of study. The flower consists of its banner or 

 " vexillum," the large upper petal, and of two side ones, its 

 " wings." Pull these off and we have left two modified petals, 

 which did not previously constitute much of the beauty of 

 the flower, and which serve a quite special object. They are 

 folded upwards to protect the reproductive organs and within 



