STKUCTURE 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.^ In con- 

 structing such diagrams it 

 will often be necessary to 

 suppose some of the parts 

 of the iiower to be raised 

 or lowered from their true 

 position, so as to bring 

 them into such relations 

 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 



A [ B C 



Via. 154. — Principal Types of Placenta. 

 At parietal placenta ; £, central placenta ; 

 C, free central placenta ; A and JB, trans- 

 verse sections ; C, longitudinal section. 



II III 



Pig. 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 ont of the calyx , 

 aronnd the pistil; III, corolla 

 hypogynous, stamens epipetalous. 



Fig. 156. — White Water-Lily. The 

 inner petals and the stamens grow- 

 ing from the ovary. 



of the white water-lily, of which a partial view of one 

 side is shown in Fig. 156.^ 



1 For floral diagrams see Le Maout and Decalsne's TraiU General de 

 Boianique, 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 

 (or this purpose. 



