A TEXT-BOOK OF BOTANY 



FIG. 214. Section of the flower of an 

 Althaea, showing sepals (a), petals 



visible from the outside, looking like two sacs, called pol- 

 len sacs. Ordinarily, therefore, the Angiosperm stamen 

 is said to have two pollen sacs. 



In most cases the pollen sacs must open so that the 

 pollen may escape, and the method of opening differs in 



different flowers. By far the 

 most common way is for each 

 pollen sac to split open length- 

 wise, and this line of splitting 

 is usually plainly seen on the 

 surface of the unopened sac 

 (Fig. 210, A). In some cases, 

 however, each pollen sac opens 

 at the top, either by a short 

 slit or by a pore-like opening 

 (Fig. 213, A and B); and in 

 some cases, as among the 



(6), tube of stamens (c) enclosing heaths, this pore-like Open- 

 style (rf), and ovules (e). After . , t 



BERG and SCHMIDT. ing may be extended into a 



more or less prominent tube 



(Fig. 213, C). There are still other special methods of 

 opening pollen sacs, but they are comparatively rare. 



In sympetalous corollas it is most common for the 

 stamens to appear fastened to the tube of the corolla (Fig. 

 208, B), and this condition is usually described as "stamens 

 inserted on the tube of the corolla." Stamens may also 

 appear united, forming a tube, as in mallows (hollyhock, 

 etc.) (Fig. 214); or they may be in two sets, as in the sweet 

 pea, in which nine of the stamens appear united and the 

 tenth one is free (Figs. 241 and 283). 



135. Carpels. It has been noted that carpels are the 

 sporophylls that be'ar the peculiar sporangia called ovules 

 ( 123). There is a striking difference, however, between 

 the carpels of Gymnosperms and Angiosperms, a difference 

 that gives names to the two groups. In Gymnosperms the 



