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 (c/. figs. 217^^ and 217^*), at 



Fig. 217. — Polleu-grains. 



1 Cohcea scandens. 2 Morina Persiea. * Cueurhita Pepo. * Passiflora Eermesina. * Circcea alpina. « Convolvulus sepium. 

 7 Cannabis saliva. 8 Pinus Pumilio. 9 Mimulus moschatus. 1° Albucca minor (dry and moistened), n Dianthus 

 Carthusianorum. 12 Corydalis lutea. 13 Gentiana rhcetica. i< Salvia glutinosa. i-s x 80-90 ; *, s, ?, *, 10 x 120-150 ; 

 11, 12 X 180 ; «, 9, 13, 1* X 220-250. 



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

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

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

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

 (fig. 217^). In Grucianella 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 

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



