98 



POLLEN. 



a hundred times greater than those of the Alpine Forget-me-not (Myosotis alpestrvi). 

 It appears also that in many flowers which remain open but a single day or night, 

 as, for instance, the Gourd and Melon, Portulaca, Morina, and the various species 

 of Mirabilis, the pollen-grains are especially big. In a single anther-cavity of 

 ilirabilis Jalapa there are, on the average, 32, and in one of Borago offi^einalis 

 60,000 pollen-grains. 



In form pollen-grains are generally ellipsoidal (c/. figs. 217" and 217"), at 



Fig. 217.— PolIen-grainB. 



I Cohma scandens. ' Morina Persica. ' Cumrbita Pepo. * Passijiora Kermesina. » Circcea alpina. « Convolvulus srpium. 

 ' CanuabLi sativa. 8 Piuus Pumilio. » Mimulvs nioschatus. '» All/ucca minor (dry ami moistened). " Didnlhus 

 Carthuskmoruin. ^^ Corydidis iutea. '^ Gentiana rhalica. i* Salna glulinasa. i-> x 80-90; <,»,',*, lo x 120-160 • 

 "," X 180; «.», IS, n X 220-260. 



any rate in quite half of all flowering plants. More rarely are they spherical 

 (figs. 217 1' 8' ''■*'^). In the liliaceous Tritelia they are narrow and lancet-shaped, 

 and in Morina (fig. 217^) biscuit-shaped. In the Pine the pollen-gi-ain possesses 

 two hemispherical bladders, and resembles an insect's head with two huge eyes 

 (fig. 217^). In Crucianella latifolia they are barrel-shaped, and in Brugmansia 

 arborea shortly cylindrical. Next to the ellipsoidal form, the angular or crystalline 

 is the commonest. Thus the pollen-grains of the Nasturtium {Tropaoliim) are 

 3-sided prisms, those of the Pansy ( Viola tricolor) 4 or 5-sided, and those of Lady's 



