238 PLANT LIFE. 



within this case, by which they are protected until mature, or 

 longer. 



These two methods of seed production form the basis for 

 the separation of the seed-bearing plants into two great groups, 

 one known as gymnosperms, or plants with naked seeds, the 

 other as the angiosperms, or plants with encased seeds. 

 Open carpels are found exclusively among the gymnosperms, 

 to which belong the cone- bearing, mostly evergreen, trees, 

 while the closed pistils are chiefly found among angiosperms, 

 to which belong the majority of garden and field plants and 

 the deciduous forest trees. 



334. The simplest form of carpel occurs in Cycas (fig. 

 245), in which the ovules are borne on the edges near the 

 bases of leaves which somewhat resemble the foliage leaves, 

 and form a whorl between preceding and succeeding whorls 

 of foliage leaves upon the main axis. The carpel of most 



gymnosperms is a scale from 

 whose upper surface arises a 

 similar fleshy scale, the pla- 

 centa, bearing two ovules 

 upon its ventral (upper or in- 



b 



Fig. 245. Fig. 246. 



Fig. 245. — An ovule-bearing leaf or carpel of Cycas re7<oluta, showing 4 ovules near 

 base, replacing the branches. On the right above, a young seed. About one quarter 

 natural size.— After Sachs. 



Fig. 246. — A young cone-scale (placenta) of Scotch pine showing the two ovules ; the 

 latter halved parallel to the scale, showing the body of ovule and the prolonged integ- 

 ument forming the micropyle, m. The scale is attached at b. Magnified about 8 

 diam.— After Kerner. 



