SOIL MOISTURE AND TO EVAPORATION. 39 



more or less nyctitropic leaves, and stems which extend upward and 

 outward for several centimeters from the summit of a long, woody 

 primary root. It is seldom possible to excavate deeply enough to dis- 

 cover the lateral roots of this plant. It grows and flowers in the driest 

 of situations, is very resistant, and, at most, loses some of its older 

 leaves at times of greatest drought. The small leaves are thick and 

 leathery and do not show the phenomenon of wilting to any considerable 

 degree. When death ensues they simply dry up and still retain their 

 positions along the basal portions of the stems until broken off by 

 external agencies. The plant used lost the main portion of its root 

 system in transplanting, but after about three weeks, during which 

 time the soil was kept well watered, growth had been renewed and the 

 plant appeared quite normal. 



Other plants which were transplanted from the ground for these 

 experiments were taken in the seedling condition. At the advent of the 

 summer rains the ground everywhere suddenly becomes almost covered 

 with seedlings of a great group of annual plants which complete 

 their generation in a single rainy season and pass the dry season in 

 the form of seeds. These plants are not especially xerophytic in their 

 structure and appear to be very much like the smaller annuals of more 

 humid regions. Immediately upon germination they send out a long 

 primary root which grows rapidly into the deeper layers of the soil. It 

 is not uncommon to find, a few days after a shower, seedlings of these 

 forms with no development of plumule and only the cotyledons and 

 perhaps a centimeter of stem above ground, while the main root is 10 

 or 20 cm. in length, still unbranched and growing rapidly downward. 

 It thus comes to be possible for such seedlings to start in the moist 

 soil following a rain and to penetrate within a short period to such a 

 great depth that they are not injured by the rapid and almost com- 

 plete drying to which the upper few centimeters of the soil are soon apt 

 to be subjected. 



The forms which were transplanted to cylinders in the very early 

 stages of their development were a species of Boerhavia, about 20 cm. 

 high at maturity, and a Tribulus brachystylis, and a single specimen 

 of Allionia incamata. Besides these plants transplanted from the 

 ground, seedlings of Fouquieria were grown directly from the seed. 

 Seeds of this plant germinate readily, the two cotyledons becoming 

 green as soon as they reach the light. The hypocotyl elongates rapidly 

 until about 2 cm. long, when this growth ceases and a slow thickening 

 begins. This growth of the hypocotyl continues for two or three 

 weeks, this organ often reaching a diameter of 3 mm. before any 

 development of the plumule occurs. This transverse enlargement is 



