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 Ga) 
out whether it is free, (Se) iC 
or axial. What ap- 
pears to be the primary 281 282 283 
9 Fics. 281-283.— Different kinds of placenta : 
office of the ovary ! 281, parietal; 282, central and axial; 283, free 
Make an enlar ge d_ central. 281 and 282 are horizontal sections ; 283, 
sketch of your speci- ‘7% 
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- 
Fie, 984,—-Hori. tanical language by saying that the flower is 
zontal diagram of a trimerous, @ word meaning measured, or 
Fe ey int. divided off, into parts of three. 
ie ae axis of 278. 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- 
