pkbsident's addeess. 129 



cylinders in Polygalacece ; dumb-bells in Umhelliferm ; and 

 triangles in Juncacece and in Gvaminca. 



Good spheres may be obtained from Abutilou and Hollyhock ; 

 ellipsoids from Winter- Aconite, Thrift, Pennyroyal, and White 

 Lily ; tetrahedrons from the tall Wood-rush ; polygons from 

 Chickweed, Bladder-campion, Nipple-wort, and Garden-pink ; 

 cylinders and rectangles from Milkwort, Heliotrope, Fuschia 

 fulgens^ and Polygala purpurea ; squares from Diplademia cras- 

 sinocla and Cestrum aurantiacum ; discoids from Cuphea platy centra 

 and Acacia ocloratissima, and dumb-bells from Iberis and Parsley. 



A few are distin-ctly peculiar in shape, thus the Mimulas are 

 curiously spiral, Rubus ccesius is prettily quatrefoil, as is also 

 C'orydaUs lutea, whilst Acacia lopliantha is tortoise-like. Now 

 aud then individual grains of peculiar form are met with as in 

 the Partridge Aloe {Aloe varieyata, PI. V., No. 7). 



Size of Poileis^ Gkains. The pollen grains examined varied 

 in diameter from one hundreth (to-o) to one twelve-thousandth. 

 (tto ott) of an inch. In my drawings a side of a square is twelve 

 milimetres, which equals -468 of an inch, and taking my low 

 power to be 59.3 diameters, the actual side of the square is 

 •00789 of an inch. 



The accompanying selection shows pollen variation in size 

 graphically, '^■' as do the following figures mathematically. These 

 dimensions are approximate: — Yegetable Marrow, "Oil 83 or 

 about 100 to an inch ; Hollyhock and most Lilies, 'OOSS-S or 

 about 120 per inch; Mallow, "00657, about 160 per inch; 

 Convolvulous, Scabious, Willowherb, and Plumbago Capensis, 

 •00526, about 200 per inch ; Abutilon, -00394, about 260 per 

 inch; Coltsfoot, '00197, about 510 per inch; Daisy, "000657, 

 from 1500 to 1600 per inch; Primula farinosa, '000329, about 

 3000 per inch ; and the smallest of all, Myosotis (Forget-me- 

 Not), '000082, or from ten to twelve thousand per inch. 



All pollen grains have a certain individual variation in size ; 

 but for each kind this limit is constant, as it is, for example, 

 among ourselves or any other living thing. It has a wider 

 range, however, in some cases than usual, as in Mahonia, Crocus, 

 White Campion, Sunflower, Passion-flower, and Salad Burnet. 



* See PI. v., Nos. 5.3-63. I 



