342 GENERAL BOTANY 



structure than that outlined above for the microsporophyll. A 

 single pistil of the marigold evidently corresponds to one mega- 

 sporophyll of the spruce, with its edges turned in and united to 

 form the ovary cavity. At the point of union of the edges of the 

 sporophyll, which form the placenta, the megasporangia, or ovules, 

 bud out and develop the integuments and sporangium proper, 

 which are characteristic of the megasporangia of the seed plants. 

 At the apex of the megasporophyll the stigma is developed, which 

 in the marigold, as in many other flowers, is furnished with hair- 

 like outgrowths for the retention of pollen. This highly modified 

 megasporophyll, or pistil, is the most universally characteristic 

 and important feature of the angiosperm flower. Such a pistil 

 as that of the marigold, which is composed of a single mega- 

 sporophyll, is called a simple pistil, to distinguish it from the com- 

 pound pistils like that of the tulip or the apple, in which more 

 than one megasporophyll enters into the composition of the 

 ovary. The compound pistil is therefore a union of several 

 simple pistils into one structure. 



It is an interesting fact that the development of a pistil in 

 the young flower of a marigold or a buttercup corroborates the 

 above interpretation of the probable origin of the closed angio- 

 sperm pistil from an open megasporophyll similar to that of 

 gymnosperms. The young sporophyll which buds out on the 

 receptacle of a developing flower of a marigold or a buttercup is 

 at first an open sporophyll resembling a rudimentary spruce 

 sporophyll but with a concavity toward the axis of the flower. 

 The edges of this concave sporophyll gradually approach each 

 other by growth and finally unite to form the ovary cavity. 

 Meanwhile the megasporangia, or ovules, bud out upon the 

 uniting edges where the placenta is to be formed, and the stigma 

 develops at the apex of the leaflike sporophyll. By further 

 growth the mature closed pistil of the marigold is formed. 



Asexual reproduction. The anther of the angiosperms is usu- 

 ally composed of four lobes, visible from the outside, which 

 represent four microsporangia. These four microsporangia are 

 shown in Fig. 202, A, as they appear in a transverse section 

 of a mature anther of a lily. In a younger anther than that 



