130 president's address. 



There is an apparent variation in size which results, in cer- 

 tain shapes, from the aspect in which the grain is viewed. 

 Ellipsoids, discoids, parallelopipedons, and cylinders show this 

 strongly, and polygonal figures in still greater variety, though 

 to a less degree. Examples of such are afforded by Lily, Pear, 

 and Groundsel ; Heath, Acacia, and Cuphea ; Heliotrope and 

 Balsam ; Sedge and Plantain ; Elm and Stellarias. 



CoLOTJE OP Pollen". For play of prismatic and complementary 

 colours, most carefully prepared experiments with costly appa- 

 ratus fall short of what nature has here provided, ready to hand, 

 for the student of the decomposition and polarization of light. 

 The colours presented arise from two causes, first and commonest, 

 from the presence of colouring matter in the grains, and second 

 from either the physical condition of the Extine or from the 

 varying refractive powers of the several constitutent parts of 

 the pollen. The colour arising from the first cause is per- 

 manent, that from the second varies with every change of focus. 

 We will therefore take them in this order. 



First, the constant colour due to the presence of pigment. All 

 may be roughly divided into ten groups, of which nine belong 

 to the first class, and the tenth to the second. This is their 

 proportion: — Colourless and more or less transparent, 12'4 per 

 cent.; white, 7-2; yellow, 47-0; orange, 10-6; brown, 5-4; 

 red, 3"2; pink to purple, 4*0; blue, 5'2; green, 2*8; and vari- 

 ous colours, complementary or prismatic, 2*2 per cent. 



The richness, translucency, purity, and brilliance of the col- 

 ours baffles description. Some of the first group are purer than 

 diamonds, some yellows excel the topaz, reds the ruby, purples 

 the amethyst, greens the emerald, blues the sapphire ; they are 

 the jewels of the vegetable world. 



The yellow and orange largely predominate, claiming about 

 sixty out of every hundred, which, coupled with the presence of 

 greens, seems to indicate that chlorophyll is responsible for the 

 colour ; and seeing that most of the remainder are browns and 

 reds, we can pretty surely conclude that iron plays a large 

 part in colouring pollen grains. The yellows and oranges range 

 from the palest conceivable colour to the deepest tints. In 



