pkesident's addeess. 133 



boss, crotchet, bead, curve, scroll, and zigzag here find worthy- 

 rivals. 



Rarely is the outline of the pollen perfectly smooth or the 

 surface uniform, but facets are presented and outlines are broken, 

 the boundary line flowing around in small or large waves, in cre- 

 nations simple or complex, in serrations deep or shallow, wide 

 or narrow. Tlie surface is usually finely or coarsely dotted 

 either by pores or pits below, or by granules or bosses above 

 the general level ; or it is ridged or furrowed generally longi- 

 tudinally, rarely transversely ; or it is covered with irregular 

 sculpturings or more often with perfectly geometrical groups, 

 breaking up the surface into such charming facets as are seen in 

 Luzula sylvatica and the Stitchworts ; or into circular or poly- 

 gonal pits with walls bounding them and all generously carved 

 or beaded, as in Armeria vulgaris and in the Lilies. 



All the variations are produced by outward or inward thicken- 

 ings of the Extine, and are best revealed respectively by the use 

 of reflected and transmitted light. Thus Begonia presents a 

 strong contrast of black and white under transmitted light, 

 whilst Cyjoripedium insigne reveals the thickenings by change 

 of tint, the yellow thin areas deepening to brown in the thick 

 bands. The facets are sometimes revealed by the play of light 

 showing variable bright spots under fine adjustment movements, 

 as in Primula farinosa. 



Both the thickness of the double cell wall and the fact that 

 the colouring matter is sometimes confined to the cell contents 

 may be revealed by the use of polarized light. Thus Fritillaria 

 under such light shows the Extine and Intine as a transparent 

 skin bounding each yellow grain. A similar result is yielded by 

 Sinajpsis arvensis. 



Outward thickenings produce ridges, bands, reticulations, suc- 

 cessive layers, bosses, and nipples, besides teeth and prickles 

 short or long, single or in groups. These latter give endless 

 variety and great beauty to the sculpturings proper. The com- 

 monest marking is a median cleft, which gives to the pollen the 

 appearance of minature anther-heads or grains of wheat. The 

 cleft is sometimes occupied by a line of cells as in Horsechestnut 



