98 



POLLEN. 



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

 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 speciew 

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

 Mirabilis Jalapa there are, on the average, 82, and in one of Borago ojfficinaiis 

 60,000 pollen-grains. 



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



Fig. 217.— Pollen-grains. 



» Cobcea scandens. * Morina Persica. ' Cueurbita Pepu. * Passiflora Eermesina. » Circcea aljiina. « Co7ivolvuliw sepi'im. 

 T CannabU saliva. ^ Pinus Pumilio. * Mimuliis inoachatiis. ^^ Albucca minor (dry aud moistened), n Z)ia«tAt« 

 Cartkusianorum. ^^ Corydalis lutea. ^^ Qentiana rhcetica. i* Salvia glutinosa. i-s xSO-90; <,«,', 6, lo x 120-150; 

 n. la xl80; «, ». is. »« X220-250. 



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

 (figs. 217 1- 3- *'^'^). 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 Brugviansia 

 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 



