98 



POLLEN. 



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

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

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

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

 MirahiUs 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.— PollBu-grains. 



iCotoaMMite™ ajfonmPemm. 'CmmriUaPepo. i Passiflom Eemiesina. ' Circosa alpina. ' ConvolviUm sepiwm. 

 ■• Cannabis lativa. » Pmus PumUw. » Ximulus moschatue. " XlJucai mmor (dry and moistened) u Dianthm 

 Carthuamnorum. i' Corydalis luUa. ^ Gentimm rhmtica. i* Salvia glutinosa. 1-8 x 80-90- *« r » w v i2(li50- 

 "," X 180; «,«, IS, " X 220-250. /vou ou, , , , , xizu-iou, 



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

 (figs. 217 1- 3. *. 8, 7). In the liliaceous Tritelia they are narrow and lancet-shaped, 

 and in Morima (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 8). In Grucianella latifolia they are barrel-shaped, and in Brugmansia 

 a/rborea shortly cylindrical. Next to the ellipsoidal form, the angular or crystalline 

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

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



