186 



ilANUAL OF BOTANY 



or arranged in a more or less regular manner. The pores 

 may be either simple, or provided with Kttle Hd-Kke processes, 

 as in the Passion-flower {fig. 388, o, o, o) and Gourd {fig. 389). 

 These processes {fig. 389, o, o) are pushed off by corresponding 

 projections of the intine, t, t, when the pollen germinates ; hence 

 such pollen-grains have been termed operculate. In the pollen- 

 grains of some of the Firs, the extine is expanded on two sides 

 to form two curious bladder-like protuberances (fig. 391). 



The poUen-grains are usually free in the loculi of the anther. 

 Sometimes, though rarely, they adhere to a greater or less 

 extent to each other. Thus we have groups of four in Periploca 

 grceca, eight in Inga anomala ; or some higher multiple of four, 



FiCf. 392. 



Fig, 39.3. 



Fig. 394. 



Fij/. 392. Polliiiia, p, of a species of Orcliis with their caudicles, e, adhering 



to the retinacula, r, r. Fig. :I93. Pistil of a species of Ascleptas, witli 



the poUinia, p, adheriug to the stigma, s. h. Pollen-masses separated. 

 Fig. 394. TJpper part of the flower of au Orchis, showing the pollinla 

 adliering to the column by the retinacula, a. 



as in many species of Acacia. In the Onagracese, the pollen- 

 grains are loosely connected by long viscid filaments or threads ; 

 while in the Orchidaoeae those of each pollen-sac cohere together 

 and form pollen-masses, to which the name oi pollinia has been 

 given {fig. 392, p). In the Asclepiadacese somewhat similar 

 masses occur {fig. 393,^, and 6) ; but in the latter, the whole 

 surface of each poUen-mass is invested by a special covering. 

 By a careful examination of these pollinia we find that they are 

 formed of definite masses agglutinated together, and when sepa- 

 rated, each of these masses is found to consist of four pollen- 

 grains. In the pollinia of the Orohidaceae we also find other 

 peculiarities ; each] is prolonged downwards in the form of 



