STRUCTURE OF THE FLOWER AND ITS ORGANS 205 
important in this way are cross-sections, which may be 
recorded in diagrams like those of Fig. 157.1. In con- 
structing such diagrams it 
will often be necessary to 
os. suppose some of the parts 
(a€) of the flower to be raised 
A B Cc 
or lowered from their true 
Fic. 154. — Principal Types of Placenta. position, so as to bring 
A. parietal placenta; B, central placenta ; h ° h bala 
C, free central placenta; Aand B, trans- them into suc relations 
verse sections ; C, longitudinal section. that all could be cut by a 
single section. This would, for instance, be necessary’ 
in making a diagram for the cross-section of the flower 
ana 
Fig. 155. — Insertion of the 
Floral Organs. 
I, Hypogynous, all the other parts on 
the receptacle, beneath the pistil ; 
II, Perigynous, petals and stamens 
apparently growing out of the calyx, Fic. 156.— White Water-Lily. The 
around the pistil; III, corolla inner petals and the stamens grow- 
hypogynous, stamens epipetalous. ing from the ovary. 
of the white water-lily, of which a partial view of one 
side is shown in Fig. 156.7 
1 For floral diagrams see Le Maout and Decaisne’s Traité Général de 
Botanique, or Eichler’s Bliithendiagramme. 
2 It is best to begin practice on floral diagrams with flowers so firm and 
large that actual sections of them may be cut with ease and the relations of 
the parts in the section readily made out. The tulip is admirably adapted 
for this purpose. 
