210 FOUNDATIONS OF BOTANY 



because the essential organs are found to be replaced by 

 petals or even by green leaves. 



The fact that leaves should be so greatly modified as 

 they are in flowers and given work to do wholly different 

 from that of the other kinds of leaves so far studied need 

 not strike one as exceptional. In many of the most highly 

 developed plants below the seed-plants, organs correspond- 

 ing to flowers are found, and these consist of modified 

 leaves, set apart for the work of reproducing (Sect. 367). 



222. Mode of Formation of Stamens and Pistils from 

 Leaves. It is hardly possible to state, until after Chap- 

 ter XXIII has been studied, how stamens stand related 

 to leaves. 1 



The simple pistil or carpel is supposed to be made on 

 the plan of a leaf folded along the midrib until its margins 

 touch, like the cherry leaf in Fig. 87. But the student 

 must not understand by this statement that the little 

 pistil leaf grows at first like an ordinary leaf and finally 

 becomes folded in. The united leaf-margins near the tip 

 would form the stigma, and the placenta would correspond 

 to the same margins, rolled slightly inwards, extending 

 along the inside of the inflated leaf-pouch. Place several 

 such folded leaves upright about a common center, and 

 their cross-section would be much like that of B in Fig. 

 154. Evidence that carpels are really formed in this way 

 may be gained from the study of such fruits as that of 

 the monkshood (Fig. 168), in which the ripe carpels may 

 be seen to unfold into a shape much more leaf -like than 

 that which they had while the pistil was maturing. What 



1 "The anther answers exactly to the spore-cases of the ferns and their 

 allies, while the filament is a small specialized leaf to support it." For a 

 fuller statement, see Potter and Warming's Systematic Botany, pp. 236, 237. 



