2O2 Plant Life and Evolution 



Many xerophytes, like the cacti and century-plant, 

 have fleshy stems or leaves with impervious outer 

 tissues, which prevent loss of water, while the 

 inner tissues are often mucilaginous and very re- 

 tentive of the moisture which is stored up in great 

 amounts. Such fleshy plants can be uprooted and 

 exposed for weeks to the hot sun before all their 

 moisture is lost. 



Bulbous Plants. Another xerophytic type is seen 

 in the bulbous and tuberous plants, which are char- 

 acteristic of many semi-arid regions like California, 

 the shores of the Mediterranean, and the Cape re- 

 gion of South Africa. These bulbs or tubers may 

 be exposed to drying up without losing their vital- 

 ity, and will be found to retain a large amount of 

 water for a long period. When proper conditions 

 arise for their growth, the leaves and flowers are 

 rapidly developed at the expense of the moisture 

 and food stored up in the bulb, and after the seeds 

 have matured, they wither away, leaving only the 

 subterranean portions alive. Many familiar garden 

 flowers are of this type, most of them coming from 

 regions with a more or less pronounced dry season. 

 California is very rich in bulbous plants, and many 

 of these, like the beautiful Mariposa-lily (Calo- 

 chortus), are among the most charming of our wild 

 flowers. 



Halophytes. Resembling in many respects the 

 true xerophytes, are the Halophytes, or salt-marsh 

 plants. Although they grow where there seems to 



