30 



BRITISH FLOWERING PLANTS 



Many leaves "sleep'' at night, that is to say, they 

 assume a position different from that taken in the day. 

 This is, however, a different phenomenon from the sleep 



Fig. 12. 



-Leaf of Clover ( TrifoKum 

 Position by day. 



Fig. 13. — Position by night. 



of flowers, and due to quite a difierent cause. As a 

 rule they turn either up or down, thus assuming a more 

 or less vertical position. This serves as a protection 

 against cold, the result being that they expose less 



surface to the sky. The 

 Acacia (Eobinia), Ox- 

 alis, Trifolium (Clover), 

 (Figs. 12 and 13) are 

 cases in point. 



Against the attacks 

 of animals leaves are 

 protected in various 

 ways : by a leathery 

 texture, by spines, by 

 felted hair, by bitter or 



Fig. 14.— Group of stinging-nettles on the arOmatic Sap, ctc. Some 

 right, and Dead-nettles on the left. t i • i 



plants, which are com- 

 paratively unprotected, mimic others which are more 

 fortunate. Thus the leaves and general habit of the 

 Dead-nettle closely resemble those of the Stinging- 

 nettle. Fig. 14 represents a group, those on the right 

 being Stinging-nettles, those on the left the white Dead- 



