140 COMPOUND ORGANS OF PLANTS. 



A fully developed leaf is composed of two parts, a little stalk 

 or support called a petiole, and a flat expanded portion called 

 the blade or limb, which is composed of woody fibre and paren- 

 chyma. The veins of the leaf constitute its woody fibre and 

 form its framework or skeleton, whilst the parenchyma is the 

 green cellular matter which fills up the interstices or intervals 

 between the veins. Now the petiole of the leaf is represented 

 in the stamen by the filament ; the midrib by the connectivum ; 

 whilst the anther corresponds to the lamina or blade, each 

 portion of the lamina, on either side of the connectivum or 

 midrib, forming an anther lobe. The pollen contained in the 

 anther-cells results from a peculiar transformation of the 

 parenchyma or green cellular matter of the leaf. 



When the stamen is destitute of a filament, the anther is 

 said to be sessile, the filament being no more essential to the 

 stamen than the petiole to the leaf. When the anther is 

 imperfect, abortive, or wanting, the stamen is considered to be 

 sterile, abortive, or rudimentary, its real nature being known 

 by its situation. 



In the stamens, the leaf undergoes such extensive structural 

 changes that its parts can scarcely be recognized. That the 

 stamens are only leaves which have undergone a greater 

 metamorphosis or change of form, nature herself teaches. All 

 will allow the analogy of the petal to the leaf. Now, the con- 

 version of stamens into petals is a common occurrence in plants 

 which have numerous whorls of stamens, especially when such 

 plants 'are brought under cultivation, as, for example, in the 

 rose and peony ; but in no plant is it seen more clearly than 

 in the flower of the Nymphsea alba, or white water-lily. In 

 this flower, perfect stamens are formed in the centre, the 

 filaments of which gradually enlarge towards the circumfe- 



