826 



ECOLOGY 



the center of the flower is the pistil (or pistils); a simple pistil or one 

 member of a compound pistil is called a carpel (g, fig. 1137). Commonly 

 a pistil is composed of an enlarged basal portion, the ovary (o, figs. 1180, 

 1181), and a slender upper portion, the style (t, fig. 1136), which is sur- 

 mounted by the somewhat enlarged and sticky stigma (or stigmas, g, 

 fig. 1136). 



Inside of the ovary are ovules (figs 581-584), which represent incipient 

 seeds, and within each ovule is the megaspore or embryo sac (figs. 582, 



FIG. 1137. A longitudinal section through the flower of a peony (Paeonia), showing 

 the calyx with its sepals (&), the corolla with its petals (c), numerous stamens with their 

 filaments and anthers (a), and the pistils or carpels (g); the broadened end of the axis 

 just below the carpels is the receptacle. From STRASBURGER. 



589), which develops into the minute female gametophyte that is char- 

 acteristic of seed plants (figs. 590-594). The entire life of the female 

 gametophyte is passed within the ovule, and after the fusion of the 

 gametes, the sexually produced spore (oospore) germinates into the em- 

 bryo, whose subsequent development is the most conspicuous feature 

 of seed formation (figs. 600-613). Usually the minute male gameto- 

 phyte begins to develop from the microspore within the anther, forming 

 a structure of two or more cells which with the persisting microspore 

 wall forms the mature pollen grain (fig. 1146). The pollen grains, 

 lodging upon the stigma, germinate, developing elongated structures, 

 known as pollen tubes, which penetrate the pistil to the female gameto- 



