The final ring of modified leaves in our typical flower constitutes the _pistil_, formed of one or many _carpels_, the essential structure of which has been touched on already (p. 82). In the present place it is desired only to point out some of the leading modifications which the pistil undergoes, so that its structure as seen by the naked eye may be understood. In the simpler forms of carpel, the affinity to leaves is still evident, though in forms of pistil made up of a number of carpels this may be very difficult to trace. With the Pea, for instance, we may begin, as presenting a very simple example. Take an oblong leaf like that of a Laurel, and fold it down the mid rib till the two edges are in contact. There is our pea-pod complete. The young seeds, or _ovules_, are borne in a row along the mid rib, a very usual arrangement. Examine next the young fruit of a Columbine (_Aquilegia_). Here there is a group of five separate erect carpels, but each is essentially like a pea-pod in structure. Compare the fruit of a Saxifrage. This clearly consists of two carpels which are grown together save at the tips, where the two styles stand out like little horns. From this we may go on to other pistils in which several carpels are completely fused together. Next, the compact body thus formed may be sunk down in the expanded top of the stem (the receptacle). Or the other parts of the flower--sepals, petals, stamens--may in their lower part be fused with the walls of the pistil, and may thus appear to spring from the top of it. In such cases the structure of the flower may easily be wrongly interpreted, and reference to a work on systematic botany is necessary if pitfalls are to be avoided. It is indeed to be noted that in flowers, as in other parts of plants, complicated structure or multiplication of parts is not necessarily an indication of advanced evolution; on the contrary, it is often indicative of a primitive condition. Just as in machinery or in organized human effort simplification often accompanies improvement, so it is with plant structures. Many of the more primitive types of flowers, such as Buttercups or Water Lilies, have a multitude of petals or stamens or carpels, while in many of the most specialized, such as Composites or Campanulas, the number of parts is much reduced. The primitive wind-pollinated flowers produce large quantities of pollen; in those which have adopted the improved method of utilizing insects, the amount of pollen is much less; in the highly specialized Orchids, a most successful group, the pollen is reduced to two small bundles.