ADAPTATION TO WATER 



161 



the stomata. The furrows are sometimes filled with hairs as an 

 additional protection, and the leaves often further reduce their 

 surface by rolling up into a thread-like shape. The leaves contain 

 also a large amount of sclerenchyma which renders water loss 

 difficult. The elongated awl-shaped leaves of J uncus and certain 



Fig. 52. A xerophytic mat plant with dissected leaves, 

 Erigeron pinnatisectus. 



Cyperacece are essentially of the grass type, though they are usually 

 not furrowed. 



Jf. The needle fnrm. This is tlie ty]ncal leaf of jhucs, s))ruces, 

 and other conifers. It is the result of a sweeping reduction of 

 leaf surface made necessary by the persistance of the leaves during 

 winter. The leaves continue to transpire at a time when the 

 available water is low on account of freezing, and serious injury 

 from drouth is prevented only by greatly reducing the amount of 

 surface exposed. The relatively small water loss from the needle 

 leaf is further decreased by a thick cuticle, and usually l)y layers 

 of sclerenchvma just below the epidermis. 



