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. 1 180, 

 1181), and a slender upper portion, the style (/, 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 fe nale 

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

 gametes, the sexually produced sp'ore (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, foming 

 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- 



