THE AISTDEOECIUM. 



63 



the openings in tlie shape of a small tubular bladder called the -pollen-tube (fig. 353) ; 

 this again soon swells, bursts in its turn, and allows the fovilla to escape in an 

 irregular jet (fig. 354). Sometimes the thin portions are circular, and surround a 

 sort of cap or covering [operculum), which is pushed off by the 

 inner naembrane [Melon, fig. 355). 



The pollen of the Cherry (fig. 354) and CEnoihera (fig. 353) opens by three pores, 

 giving passage to three pollen-tubes ; that of the Melon {fig. 355) by pushing off six 

 discoid caps, which open like doors, or are completely removed by the pollen-tube. 

 In Pine pollen (fig. 356) the outer membrane splits into halves by the distension of 

 the inner. The pollen ot Polygala (figs. 357, 358) resembles a little barrel, of which 

 the staves, formed by the outer membrane (e), open by longitudinal clefts to allow 

 of the passage of the inner membrane (p). The pollen of Orchis (fig. 359), instead of 

 being powdery as in the previous cases, is composed of two waxy masses [massm pol- 

 linis) supported on two small elastic stalks, named caudicles [caudiculi), and resting 

 on a flat glandular base, called the retinaculum. ; 

 these masses present a series of small angular 

 corpuscles [massuloe) joined by an elastic network, 

 continuous with the caudicle ; each corpuscle again 

 is formed of four pollen-grains, and each pollen- 

 grain consists of a single membrane, which lengthens 

 into a long tube containing the fovilla (fig. 360). 

 The retinaculum is a portion of the anterior face of 

 the style ; it secretes a viscous fluid, which agglu- 

 tinates the originally fre'e pollen-grains ; this viscous 

 fluid is infiltrated between the grains, and adheres 

 to them, then hardens, and forms the network which 

 unites the grains together, and to the small stalk which bears the 

 network (fig. 359). 



The pollen of Ascl&pias (fig. 361) is very analogous to that of 



Orchis ; the five bilocular anthers are introrse, and rest against the 



Poiieii mass and sides of the stigma, which has five rounded angles ; each cell contains 



a compact mass of pollen, the grains of which are provided with a 



single membrane, and are closely united. At each angle of the stigma, between each 



pair of stamens, are two small viscous bodies [retinacula), from each of which a furrow 



361. Ascleplas. 

 Pistil and pollen masse=; 

 adhenng to the stigma. 



