I'EGETA TH'E REPRODUCTION. 237 



include both sorts of sporophylls. The perianth may be com- 

 posed of one or two kinds of leaves, often bright-colored. If 

 there are two sorts, those next the sporophylls are generally 

 highly colored, and constitute the corolla. Each leaf of the 

 corolla, when distinct, is a petal. The leaves below the co- 

 rolla are often green. They constitute the calyx, and each, 

 when distinct, is a sepal. 



331. Carpels.- The leaves (sporophylls) bearing the 

 ovules (megasporangia) are called carpels. They may be 

 flattened ; or so curved that in the course of their develop- 

 ment the edges unite and a cavity is more or less perfectly 

 enclosed ; or neighboring carpels may grow together in such 

 a way as to form a case. Such hollow structures, whether 

 composed of one or more carpels, are often somewhat pestle- 

 shaped, whence they early received the name pistil (fig. 244). 

 A flower whose only essential organs are pistils is called pis- 

 tillate. The sporangia arise usually upon the ventral (inner) 

 face or the edges of the carpels. In the open carpel they are 

 exposed, but in the closed carpels they are completely shut 

 in, except for a narrow opening which sometimes remains, by 

 which the interior cavity communicates with the outside air. 



332. Ovules. Among seed plants the sporangia which the 

 carpels bear are universally known as ovules, a name given to 

 them under the supposition that they were the eggs which, 

 upon fertilization, produce new plants. Though they are not 

 in any respect comparable to the real eggs (since they are 

 produced by the non-sexual or sporophyte phase), the name 

 is retained for convenience. 



333. Gymnosperms and angiosperms. When the changes 

 through which the ovule passes are complete, it becomes the 

 seed. When the ovules are produced upon the free surface of 

 an open carpel, the seeds are, therefore, exposed. On the 

 contrary, when the ovules are borne within a closed pistil 

 (formed by one or more carpels) the seeds are developed 



