THE PISTIL. 95 



VALVES the parts into which carpels separate by de- 

 hiscence (Fig. 319). 



PLACENTA the cord along the ventral suture to which 

 ovules are attached. 



Point out and name the various kinds of pistil shown 

 upon the charts. 



EXERCISE XLII. 

 The Structure of Ovaries. 



Whether a pistil is simple, multiple, or compound, each 

 carpel may be looked upon as a single leaf. The simple 

 pistil of the pea, for instance, may be regarded as the 

 blade of a leaf folded at the midrib, so that its inner por- 

 tion answers to the upper face of a leaf, and its outer por- 

 tion to the under face. Its dorsal suture will correspond 

 to the midrib, and its ventral suture to the margin of the 

 leaf. 



To make this plainer, take any strong oblong leaf (Fig. 

 285), and fashion it into a carpel, like the pea-pod, taking 

 the upper part of the leaf for the inner part of the carpel. 

 Fold in the margins slightly to represent the placentae 

 (Fig. 286). If the fold will not stay in place, take a stitch 

 or two along it with a needle and thread. Now fold it 

 together at the midrib (Fig. 287), and compare it with a 

 pea-pod. Find the valves ; the dorsal and ventral por- 

 tions ; the stigma ; the base. 



Gather old, faded pea-blossoms, in which the ovary is 

 somewhat enlarged, and observe that the ventral suture is 

 turned inward ; that is, it lies along the central line, or 

 axis, of the flower. It is along this axis, then, that the 

 double placentas are formed. Observe the position of the 

 dorsal suture, or back of the pod. It is important to bear 

 in mind that, in the case of the simple pistil, the ovules 

 are attached centrally along the axis of the flower. 



Roughly to imitate a multiple pistil, you have only to 

 bind together, by their petioles, several leaf-blades that 

 6 



