82 PART I. — ORGANOGRAPHY. 



ovules ; but in most flowering plants it forms a closed sac which 

 envelops and protects them. Pistils of the former kind are 

 called gymnospermous ; they are usually quite simple in their 

 structure ; those of the latter kind are termed angiospermous, 

 and they exist in a great variety of forms. When complete, 

 an angiospermous pistil consists of ovary, style and stigma. 



The ovary, usually the basal portion, is the part which con- 

 tains the ovule or ovules ; the stigma, commonly the apical por- 

 tion, is the part which receives the pollen, and the style the part 

 which connects the ovary and stigma, Fig. 256. The former two 

 are essential, while the latter is not. When the style is wanting, 

 as is frequently the case, the stigma is said to be sessile. 



The pistil, though greatly changed from the ordinary form of 

 the leaf, still in many cases clearly shows its relationship to one, 

 and it is possible for us to trace the correspondence of parts. 

 If we imagine an ordinary leaf, like that of the Cherry, to be 

 folded in such a manner as to bring the upper surface and mar- 

 gins interior, as in Fig. 255, the lower portion would correspond 

 to the ovary, the infolded margins projecting into its cavity to 

 the ovule-bearing portion, ox placenta, the apical portion to the 

 stigma, and the narrow upper portion of the leaf adjacent to it, 

 to the style. If the ripe follicle of the Columbine or of the 

 Caltha be opened out, as in Fig. 257, the correspondence in 

 structure to the infolded leaf above described, will be at once 

 evident. That this is the real nature of the pistil is further 

 shown by the study of its development, and by the study of 

 monstrous forms of it, in which we often find more or less com- 

 plete reversion, or return to the ordinary condition of a leaf. 



If a Pea-pod be carefully laid open and examined, the young 

 peas will be found to occupy a double row along one of the 

 sutures of the pod, as illustrated in Fig. 258. This portion cor- 

 responds to, the infolded edges of the leaf, and when the pod 

 splits open it does so along the line separating these edges. This 

 line is called the ventral suture. But it also dehisces along the 

 opposite side, called the dorsal suture, and this corresponds to 

 the mid-rib of the leaf. A leaf thus transformed into an ovule- 

 bearing organ is commonly called a carpel or carpophytl, and the 

 pistils of the Caltha, the Columbine and the Pea are each made 

 up of single carpels. Such pistils are described as apocarpous. 



