STRUCTURE.] MORPHOLOGY OF STAMENS. 349 



extended form. A leaf consists of a midrib, on each side of 

 which is a parenchymatous expansion, consisting of a double 

 stratum of tissue, separated by vessels. In the anther the 

 midrib assumes the form of the connective ; the double 

 stratum on each side of the midrib is, at the centre, developed 

 in the form of pollen, and hence the primitive quadrilocular 

 structure of the anther, as above described. The line of 

 dehiscence in ordinary circumstances is the margin of the 

 modified leaf. Schleiden makes this additional remark : 

 " The normal leaf, as is well known, exhibits upon its upper 

 surface cellular tissue, different in structure from that on the 

 under ; to this we find that the pollen of the anterior and 

 posterior cells of the anther corresponds. It may, perhaps, 

 be possible, and certainly would not be uninteresting, to 

 ascertain, by experiment, whether or not the pollen of one of 

 these compartments only possesses the external characters * 

 of pollen, and likewise different functions in the process of 

 impregnation, or whether in dioecious plants one kind would 

 produce male, the other female embryos." 



Agardh considers a stamen to be composed of two leaves in 

 a state of adhesion ; and that it is in fact a bud axillary to 

 a sepal or petal. This is very nearly the opinion formerly 

 entertained by Wolff. Endlicher adopts this view to a certain 

 extent ; and supposes the leaves to be rolled backwards, so 

 that their under surface becomes the polliniferous part. But 

 all this is mere hypothesis, unsupported by evidence, and in 

 opposition to the direct observations of Mirbel and Schleiden. 

 The latter well observes, that the stamens are evidently 

 modified simple leaves, for they constantly appear at a later 

 period than the petals, although they afterwards develope 

 themselves more rapidly ; they stand at first higher up upon 

 the axis than the preceding circle of corolline leaves, and they 

 alternate invariably with them. 



Such is the structure of the stamens in their perfect state. 

 It often, however, happens that, owing to causes with which 



* It is so expressed in the translation in Taylor's Magazine ; in the original 

 it is ; " ob vielleicht der pollen einer von beiden, nur der form nach pollen sei, 

 und bei der befruchtung sich verschieden verhalte," u. s. w. 



