420 



HUTCHINSON'S POPULAR BOTANY 



of an ounce of the fluid has been found 

 in one of these receptacles. 



So much for Nectaries. We have 

 now considered five of the means by 

 which insects are attracted to flowers 

 with a view to the transference of 

 pollen, and only one remains to be 

 spoken of. The five already treated 

 are Conspicuousness, Odour, Irregu- 

 larity, Honey-guides, and Nectar; 

 the sixth is the fecundating dust 

 itself. 



In the majority of insect-pollinated 

 flowers the pollen-grains are either 

 rough or sticky, and thus are distin- 

 guished from the pollen-grains in wind- 

 pollinated flowers, which are usually 

 smooth. The reason of this is obvious. 

 The rough and sticky kinds " clinging 

 pollen," as Kerner calls them are 

 adapted for clinging to insects visiting 

 the flowers ; the smooth kind dusty 

 pollen is not less adapted for disper- 

 sion by the wind ; for being easily 

 taken up by the slightest breeze, and 

 having no inequalities of surface, its 

 resistance in passing through the air is of the slightest. 



Few objects are so beautiful under the microscope as the pollen-grains 

 of flowers. Not only do they vary greatly in their general forms, but 

 their walls in many instances show the most exquisite sculpturing and 

 patterns, which if animals of the lower creation are as susceptible to 

 beauty of form as man must delight the eyes of the insects engaged in 

 transporting the pollen from flower to flower. We may draw attention 

 to an example here and there. Each spherical grain of the Passion-flower 

 (Passiflora, fig. 494) looks under a strong magnifying power like a beautifully 

 chased Indian bowl. In Lapageria, Cucurbita (the Gourd family, fig. 493), 

 and not a few other plants, the spherical grains are covered with spines. 

 In the Scots Pine (Pinus sylvestris, fig. 495) each grain is provided with 

 a pair of bladder-like wings, which stand out from the grain like goggle- 

 eyes. As the pollinating agent in this plant is the wind, the bladder-like 

 structure is a most useful contrivance. 



In a good many plants, as the Evening Primrose (CEnothera biennis, fig. 

 492), Clarkia, Fuchsia, etc., clinging pollen is strengthened by the presence 

 of a sticky, structureless substance called viscin, which causes the grains to 



FIG. 523. TWAYBLADE (Listera ovata). 



(a) Labellum ; (n) grooved nectary ; (s) stigma ; 



(r) rostellum ; (p) pollinia. 



