THE OAK TRIBE. 141 



falling on the stigma of the other, and fertilizing it, 

 unless an unusual quantity of stamens was provided ; 

 hence it is that in a fine day in spring the whole air 

 is, as I have just said, so impregnated with particles of 

 pollen, that they cover every thing as with a fine dust. 

 By degrees, as warm weather advances, the pro- 

 tection of the scales of the bud ceases to be necessary 

 to the young flowers, which swell and burst through 

 them ; the involucre daily grows larger ; the stigmas 

 having fulfilled their destiny, shrivel up ; the ovary 

 enlarges ; one of its ovules grows much faster than 

 the other, and gradually presses upon it till it smo- 

 thers it ; the shell hardens, an embryo makes its 

 appearance, and by degrees fills up the cavity ; and 

 at last you have a perfect nut, with its husk (Jig. 8.), 

 or involucre. At the point of the nut is to be seen 

 the remains of the calyx (Jig. 9- b.) ; but no trace 

 can be found of the cell and ovule which were smo- 

 thered ; so that a one-celled fruit is produced by a 

 two-celled ovary. You will now know whv nuts 

 sometimes grow in clusters, and sometimes singly ; 

 if cold or accident should destroy any part of the 

 cluster of pistils in the bud, but a very few nuts, per- 

 haps only one, will grow and ripen ; but if they are 

 mostly saved, you will then have the large clusters 

 which are so common in seasons which have been 

 preceded by mild springs. The nut itself affords an 

 excellent illustration of the structure of a dicotyle- 

 donous embryo ; the two great fleshy lobes into which 

 the nut separates when freed from its skin (Jig. 9. c), 



