306 



NATURAL EISTOBY OF PLANTS. 



outer surface naked or bearing certain projections whose nature we 

 shall examine below. The superior opening of this sac is sometimes 

 circular and simple ; sometimes double, presenting an outer rounded 

 rim, entire, or cut up into crenulations, festoons, or even lobes of 



Siparuna guianensis. 



> 



Fio. 352. 

 Male flower {}f). 



Fig. 353. 

 Loncitudinal section of male flower. 



Fig. 354. 



Longitudinal section of female flower. 



Fig. 355, 

 iOngitudinal section of fruit (^). 



variable depth, and within this rim a " velum'' or sort of conical roof, 

 raised or depressed, sometimes nearly flat and horizontal. In the 

 centre of this diaphragm is an opening, usually narrow, and some- 

 times reduced to a simple circular pore on anthesis. This gives 

 passage to the stamens or to tlie stigmatiferous summits of the 

 styles, as the case may be, while the lower parts of the reproductive 

 organs remain shut in by the perigonal sac, towards the bottom of 

 wliich they are inserted (Hgs. 352-35 1). 



Tlie characters of the androceum are peculiarly variable in Sipa- 

 runay but as we find gradual transitions between the ditVerent 

 variations we are about to mention, it has been altogether impos- 

 sible to split up the genus on that account. The stamens may be 

 very numerous in some species, such as S. ncyU'da &c., while in 



