ELEMENTS OF STRUCTURAL BOTANV. 9 



halves of the leaf, and tlie cells burst open along what 

 unswers to the margin of the leaf. 



10. In the case of apocarpous pistils, as that of the 

 Buttercup, the botanist considers each carpel to be 

 formed by a leaf-blade doubled lengthwiie until the 

 edges meet and unite, thus forming the ovary. Fig. 13 

 will make this clear. 



11. There are many facts which support this theory 

 ao to the nature of the different parts of the flower. 

 Suffice it to mention here, that in the Avhite Water- 



Lily, in v, hich there are several circles of sepals 

 and petals, it is difficult to say where the sepals 

 end and the petals begin, on account of the 

 gradual change from one set to the other. And 

 Fig. 13. ^ot only is there a gradual transition from se- 

 pals to petals, but there is likewise a similar transition 

 from petals to stamens, some parts occurring, v/hich are 

 neither altogether petals, nor altogether stamens, but a 

 mixture of both, being, imperfect petals with imperfect 

 anthers at their summits. We can thus trace ordinary 

 leaf-forms, by gradual changes, to stamens. 



We shall, then, distinguish the leaves of j^lants as 

 foU a ije -leaven, and jluiver-kaves, giving the latter name 

 exclusively to the parts which make up the flower, 

 and the former to the ordinary leaves which grow 

 upon the stem and its branches. 



12. You are now to try and procure a Buttercup 

 whose flowers, or some of them, liave withered awav, 

 leaving only the head of carpels on the receptacle. The 

 carpels will have swollen considerably, and will now 

 show themselves much more distinctly than in the 



