VEGETA TIVE REPRODUCTION. 



••15 



placenta in angiosperms commonly consists of a cushion of 

 tissue usually at the united edges of the carpel or carpels, [f 

 the carpels are united into a compound pistil, the placentas 

 will be cither isolated, as ridges upon the inner face of the 

 wall of the ovulary (fig. 25 2 J, 

 or aggregated at its center 

 (fig. 251). Occasionally the 

 ovules arise upon the entire 

 inner face of the carpels, as in 

 the gentians. 



Fig. 257. 



Fig. 258. 



Fig. 257.— A median longitudinal section through the flower of Klu-um undulatutn, 

 s, a sepal; /. a petal; n. a, n, anthers; «, stigma; /. ovulary; kk, sporangium, 

 which, with the two integuments over it, forms the single ovule terminating the axis ; 

 </>; nectary Magnified about 10 diam. — After Sachs. 



Fig. 258. -Pimpernel lAmtgnUu arvensis). A, median longitudinal section ol a 

 young flower-bud ; /.sepal; c, corolla, just beginning to develop ; .(.anther; A", car- 

 pels growing over A. tne apex ol the axis. />', median longitudinal section ol the 



pistil. . . the carpels, forming a root over S, the axis on which ovules are beginning 



to develop, and growing up to form a columnar style at whose apex is the stigma, '.. 

 (', the same, older. ,S, the enlarged apex of the axis showing six ovules, Sk, in sec- 

 tion; gr. the style: n, the stigma, on which arc lodged pollen grains, p. All magni- 

 fied.— After Sachs. 



344. Stamens.— A stamen is a leaf (sporophyll) of the 

 seed plants which bears the microsporangia, or pollen sacs. 

 The flowers whose essential organs are all stamens are said to 



