PEESIDENX'S ADDKESS. 125 



irregular, smooth, toothed or beaded, presenting an almost end- 

 less variety of aspect, and giving great beauty of form and 

 tracery to the grains. Some of these projections certainly answer 

 some functional purpose, thus the Anemophilous pollen of Pines 

 and of some other Conifercb have two vesicular hollow bodies 

 which help their flight. 



Pollen cells are not generally filled with protoplasm, indeed 

 usually the protoplasm merely lines the inner face of the Intine, 

 throwing bridges or plates from side to side of the cell, through 

 the cell-sap which distends the cell-walls. The Intine during 

 the process of fertilization protrudes through either an orifice or 

 a thin place in the Extine, and developes the fertilizing pollen- 

 tube by which the protoplasm and cell-sap forsake the cell, which 

 then dries up, and passes to its " Ultima Thule," the ovule. 



The Extine is outwardly rarely smooth or even, but is gene- 

 rally striated, ridged, sculptured, or ornamented with projections 

 very varied in form and size. Whatever character the outer 

 surface of the Extine presents is clearly dependent, partly at 

 least, on the mode by which the pollen is to be conveyed to the 

 female organ, or whether cross-fertilization or self-fertilization 

 is desirable. All externals of the Extine, except perhaps pure 

 ornamentation, must be looked upon as accessories to the final 

 purpose of the pollen, although their exact duties cannot be 

 assigned them in every case. Those which are wind-borne, 

 anemophilous, or fall through the air, are angular, very dry and 

 often smooth, as Quercus Rohur, Aconitum Napellus, Poa pra- 

 tensis, and Irish Yew. Others shine like glass beads or polished 

 silver, as Viola odorata, CorydaUs lutea, Allium ursinuni, and 

 Cyclamen, which are probably more independent. Some even 

 which are prickly, look as though they were glazed, as Cucurhita 

 ovifera. The common occurrence and great variety of prickles 

 may be taken as proof that they play an important part in secur- 

 ing pollination. Thus those that are insect-borne, entomophilous, 

 possess either hairs, as the Ragworts, Campanulas, Cacti, etc. ; 

 or coarse prickles or spines, as Coltsfoot, Dahlia, Sunflower, and 

 the QompositcR generally ; or if massed, have a special secretory 

 organ, as the Rostellae of some Orchid pollinia like Oncidium 



