84 THE STAMEN A SPOROPHYLL [CH. 



like stamens present obvious leaf-like characters, while in 

 the common Indian Shot one flat, petal-like organ alone 

 bears an anther lobe at one of its edges. In another 

 class of cases we find stamens metamorphosed into carpels 

 or petals, or even into green leaves, and this in a few in- 

 stances is traced to the action of parasitic organisms ; 

 while cases are known of buds arising in the axil of the 

 stamen of a flower, though such events are rare and 

 abnormal. 



Such more or less exceptional cases of transition and 



' metamorphoses by no means suffice by themselves to prove 



that a stamen is a leaf; but they suggested the homology 



to the older naturalists, and when all the facts are taken 



into account there can be no further doubt on the subject. 



Thus, the insertion of the stamens in the less modified 

 types of flower is like that of leaves, and a vascular- 

 bundle passes out from the floral axis up the filament as 

 in the case of a leaf. Again, the anther is covered by an 

 epidermal layer, and in some flowers (e.g. Lilium) well- 

 developed stomata are found in this. 



It is in the development of the stamen, however, that 

 the clearest evidence of its leaf-nature is obtained, and 

 when this is compared with all we know of the develop- 

 ment and structure of leaves elsewhere the homology is 

 unassailable. Since we shall find that pollen-grains are 

 spores, moreover, we have to understand that the stamen 

 is a spore-bearing leaf i.e. a Sporophyll quite like that 

 of many of the Cryptogams. 



In the typical stamen the prolongation of the filament 

 between the anther-lobes is called the connective, and the 

 lobes themselves are often termed thecce : each theca may 

 have two pollen-chambers or pollen-sacs or only one, and 

 in the latter case the single chamber usually arises by the 

 fusion of two. 



