616 D. T. MACDOUGAL 
slender central cylinder and a thick inclosing cylinder of thin- 
walled tissue have been alluded to in this connection, but these great 
Fic. 4.—Aspect of the vegetation in regions with no well-marked rainy seasons of 
regular recurrence. (Above) The bolson of Las Vegas, Nevada. (Below) Bajadas of 
minor range of mountains near the shore of the Gulf of California, San Felipe Bay. 
The plants comprise spinose forms with very reduced shoots and leaves, which have 
not developed storage capacity. 3 
sporophytes probably stood in swamps, or at least were hygrophytic 
in habit, and by the requirements of their separated gametophytic 
a 
