l6l2 



A TEX'l'BOOK OF THEORETICAL BOTANY 



leaves on the long shoots. They are often trifid and in their axils arise 

 short shoots bearing normal leaves. 



The common Barberry was largely exterminated in Britain during the 

 eighteenth century, following the discovery that it was the alternate host 

 of the Stem Rust of Wheat, Puccinia graminis, and the extermination of 

 the host plant is now being strenuously attempted in the Wheat Belt of 

 North America. 



The genus Epimedium (Fig. 1465) with dimerous flowers, also has an 

 interesting pollination mechanism. The flowers are protogynous and the 

 nectar is concealed. The anthers dehisce by valves (Fig. 1466) which come 



Fig. 1466. — £'/)/we(//;</;/, pollination. A - C. Longitudinal sections of the flower 

 showing the nectaries and the valvate dehiscence of the anthers. D - F. 

 Dehiscence of a single anther, enlarged. (Stages from right to left.) 



together above the already mature stigma. They cannot, however, pollinate 

 it because, at this stage, the flowers, which are borne in a raceme, are 

 pendulous. Nectar is secreted in four shoe-shaped nectaries, together 



