and 4). Beneath the cuticle is a thick layer of water- 

 storing cellulose. A series of forms with this type of 

 stoma arranged in order of progressive sinking of the 

 stoma would include: Hesperaloe prccciosa, Yucca de 

 smetiana, Y. rupicola, Agave strida and Dasylerion 

 texanum. In the last named (Fig. 5) the supra-stomal 

 passage is divided into two dead air spaces, and the 

 stomata occur in slight longitudinal furrows. The ridges 

 between are braced heavily with mechanical tissue. 



In Agave americana, the century plant (Fig. 6), the 

 sides of the elongated supra-stomal passage are produced 

 into lips, constricting it in the middle. 



