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.! 
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. 
