Establishment Behavior oi? the Palo Verde. 295 



The arid after-summer and the arid fore-summer are found 

 to give rise to the greatest number of deaths, while the winter 

 season and the humid mid-summer season give rise to a lesser 

 number. The 62 seedlings surviving at the end of sixteen months 

 are 11% of the original number of germinations. What the fate 

 of these survivors will be may be inferred from the results of an 

 examination which I made of all the dead seedlings which oc- 

 cupied my observational area when I began work on it in May, 

 1910. These represented, presumably, the ('eaths of the preced- 

 ing 12 to 18 months, being 160 in number. After a prolonged 

 soaking in ghcerine and alcohol the seedlings were sectioned 

 and their ages determined, with results as follows: 



Age in years 1 2 3 4 5 6 7 8 9 10 

 Number 105 32 20 1 1 1 



These figures indicate, as "\\ould be anticipated, that the 

 greatest mortality occurs in the first year, that it continues at a 

 rate \\ hich is high relatively to the number of survivors through 

 the second and third years, and falls thereafter to a rate which 

 is very low. The number of survivors at the end of the third 

 year is probably never more than 3% of the number of germina- 

 tions, and must often be none at all. 



I have noticed that the severely arid conditions of the fore- 

 summer cause the death of a great many twigs on Palo Verdes 

 that must be from 10 to 20 years old, and on all sizes larger than 

 that. The death of these twigs of coirrse serves to cut down the 

 water requirements of the plant a|j^ must operate in the direc- 

 tion of saving the remaining portion of the plant at a time of 

 extreme transpiration and very dry soil. It is, iir effect, anala- 

 goirs to the leaf-fall of the decidious trees in the dry rrronths of 

 morrsoon climates, and is more crudelv analagous to the con- 

 traction of volume under severe transpiration that is exhibited 

 by the larger cacti. When a Palo Verde seedling becomes large 

 enough to withstand the loss of some of its branches in the most 

 critical portion of the year, its life is safe from all but droughts 

 of the most extreme severity. When this age is attained, and it 

 must be a variable one, the death rate falls to an extremely low- 

 figure. I have had a great many thousands of Palo Verdes come 



