Flowers. 151 



123. Make cross and vertical diagrams of the flower as 

 in c and d, Fig. 74, showing clearly the number, relation- 

 ships, and relative positions of the parts. The cross dia- 

 gram shows the number of the parts and their relative 

 positions, while the vertical diagram shows the attach- 

 ment, direction, and to a certain extent the form of the 

 parts. 



In drawing the cross diagrams a pair of cheap dividers 

 carrying a lead pencil will be a great help in placing the 

 different whorls of parts symmetrically. The guide circles 

 should be made with a light touch, making first the central 

 circle a, A, Fig. 77, for the ovary, and then the circles b^ 

 c, and d for locating the stamens, petals, and sepals. Draw 

 dotted or very faint lines, as in B and C, to locate the 

 position of the walls of the ovary. Then outline the cavi- 

 ties of the ovary, taking care to show the right relative 

 thickness of the outer and partition walls of the ovary, as 

 in D and E. If the placentae are central, as in D, the 

 place of attachment of the ovules should be left blank (see 

 cavity e, D} until the cavities are outlined ; then the ovules 

 are to be outlined by continuing the ends of the interrupted 

 line (/ and g, D). If the placentae are parietal, proceed 

 according to diagram E. 



Place points on the outer circles to locate the positions 

 of the stamens and the centers of the petals and sepals, as 

 in A. If the dividers are set to swing guide circles having 

 diameters the same as those of the half circles on the pro- 

 tractor (Fig. 84), the guide circles may quickly be divided 

 into the required number of equal parts. Suppose, for 

 example, that the guide circle has the same diameter as 

 the half circle c, and it is desired to divide the guide circle 

 into five equal parts ; place one point of the dividers at 

 c on the zero line and the other on the circumference c, 



