FLOWERS OF IMPATIENS FULVA 165 



nearly filling the diminutive pollen sac. The anthers dehisce (Fig. ZZ) 

 but the pollen grains are not discharged from the pollen sacs. They 

 germinate within the sac and the pollen tubes pass through the stomium 

 directly down to the stigmatic surfaces below. Thus, although there 

 is a great reduction of pollen, there is also a great reduction in the 

 amount of waste. 



This reduction of parts in the anthers is common to cleistogamous 

 flowers. In /. noU-tangere the pollen sacs are small, not containing 

 more than forty or fifty pollen grains. An endothecium is present and 

 dehiscence occurs, but the grains germinate in the pollen sacs and the 

 pollen tubes pass out to the stigma below (26 p. 53). In Oxalis acetosella 

 "the number of pollen grains in each loculus may not exceed two 

 dozen" (26). Helene Ritzerow (41) gives a summary of conditions in 

 various cleistogamous flowers, listing species in which the various condi- 

 tions occur. In not a few species a reduction in the number of stamens 

 occurs. Perhaps the occasional occurrence of one or two shorter stamens 

 in fulva is a tendency in this direction. In the majority of species 

 there is a tendency to reduction in the number of pollen sacs from four 

 to two. An endothecium is present in all cases except in Amphicarpaea. 

 In the majority of species, the pollen grains germinate in the anthers; 

 in a few they fall out and germinate on the pistil. The pollen tube may 

 pass directly through the wall if the endothecium is absent or does not 

 open, if it opens they pass through the opening. 



Development of the Pollen 



The development of the pollen is the same in each type of flower. 

 The archesporial cells were first recognized when separated by one parie- 

 tal layer, from the epidermis (Fig. 10). One or two cells appeared thus 

 in the cross sections of the young anther lobes. In longitudinal sec- 

 tions these appeared as a plate of cells one layer in thickness. The 

 primary parietal layers divide to form four or five layers. The outer- 

 most parietal layer, immediately under the epidermis, becomes differen- 

 tiated as the endothecium. The tapetum arises as a single layer from 

 the sporogenous cells. This primary tapetal layer later becomes a 

 double tapetal layer (Figs. 11 and 12). By the time the sporogenous 

 cells have arrived at the mother-cell stage the tapetum shows signs of 

 flattening as if through crushing by the sporogenous mass, or by breaking 

 down to furnish nourishment for the developing spores. By the time 

 the tetrad stage is reached the tapetum and one, two, or three parietal 

 layers have collapsed (Fig. 12). Before the mother-cell stage is reached 



