THE FLOWER 



201 



is parietal; if to a central axis formed by the edges of the 

 carpels projecting inwards (Fig. 282), it is central and axial ; 

 if instead of being attached to the carpels, the ovules are 

 borne on a projection from the receptacle, the placenta is a 

 free central one (Fig. 283). If your cross section shows a 

 central placenta, make 

 a vertical cut down to 

 the receptacle and find 

 out whether it is free, 

 or axial. What ap- 



281 282 283 



FIGS. 281-283. Different kinds of placenta : 

 281, parietal; 282, central and axial; 283, free 



pears to be the primary 

 office of the ovary? 



Make an enlarged central. 28 1 and 282 are horizontal sections ; 283, 

 i , i / vertical. 



sketch of your speci- 

 men in both vertical and horizontal section, labeling correctly 

 all the parts observed. 



217. Numerical plan. --Make a horizontal diagram 

 of the plan of the whole flower, after the model given in 

 Fig. 284, showing the order of attachment of the different 

 cycles, sepals, petals, stamens, and pistils, the number 

 of organs in each set, and their mode of alternation with the 

 organs of the other cycles. Notice that the 

 parts of each set are in threes, or multiples 

 of three. This is called the numerical plan 

 of the flower, and is the prevailing number 

 among monocotyls. It is expressed in bo- 

 FIG 284 Hori- tanical language by saying that the flower is 

 zontai diagram of a trimerous, a word meaning measured, or 



flower of the lily kind. v i i /v j / it 



The dot represents divided off, into parts of three. 



2 1 8. Vertical order. Next make a ver- 

 tical diagram of your specimen after the 

 manner shown in Fig. 269, and note carefully that the ovary 

 stands above the other organs (this is true of all the lily 

 family), and is entirely separate and distinct from them. In 

 such cases the ovary is said to be free, or superior, and the 

 other organs inferior, or hypogynous, a word meaning "in- 



the growing axis of 

 the plant. 



