98 



POLLEN. 



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

 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 

 Mirabilis Jalapa there are, on the average, 32, and in one of Borago officinalis 

 60,000 pollen-grains. 



In form pollen -grains are generally ellipsoidal (cf. figs. 217 13 and 217 14 ), at 



Fig. 217. Polleu-graing. 



Cobcea scandens. * Marina Persica. * Cueurbita Pepo. * Passijlora Kermesina. * Circcea alpina. Convolvulus septum. 

 7 Cannabis sativa. 8 Pinus Pumilio. 9 Mimulus moschatus. 10 Albucca minor (dry and moistened). 1* Dianthus 

 Carthusianorum. 12 Corydalis lutea. " Gentiana rhcetica. M Salvia glutinosa. i- x 80-90; *, 8 , ', 8 , 10 x 120-150 ; 

 11, i X180; , , , i* x 220-250. 



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

 (figs. 217 1 ' 3 ' 4>6>7 ). In the liliaceous Tritelia they are narrow and lancet-shaped, 

 and in Morina (fig. 217 2 ) biscuit-shaped. In the Pine the pollen-grain possesses 

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

 (fig. 21 7 8 ). 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 (Tropceolum) are 

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



