84 



THE LIVING CYCADS 



adapted to keeping the opening closed except when the 

 air is full of moisture. Long, narrow cells with thick, 



Fig. 30. — Dioon spinulosiim at Tierra Blanca, Mexico; plants grow- 

 ing on rocks with little soil, showing exposed roots; at the right the base 

 of a trunk with an exposed root (+) nearly as large as the trunk itself. 



