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^* and 217^*), at 



Fig. 217.— Pollen-grainB. 



» Cobcea scandeng. » Morina Persica. • Ctuuriita Pepo. * PasBifiora Kermeeina, • Circcea alpina. • Convolvulus sepHm. 

 7 Cannabis sativa. * Pinu3 PumUio. » Mimulus moschatus. " Albucca minor (dry and moiBtened). " Diaiitkus 

 Carthusianorum. i^ Corydalis lutea. i' Gentiana, rhmtica. ^* Salvia glutinosa. i-» x 80-90; *,», f, », w x 120-160; 

 11, 12 X180; t, », i», 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 poUen-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 elHpsoidal form, the angular or crystalline 

 is the commonest. Thus the pollen-grains of the Nasturtium (Tropoeolvm,) are 

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



