DEPARTMENT OF BOTANICAL RESEARCH. 57 



tion of the beaches ; but it acts as a great cooperating force by carrying clouds 

 of winged seeds to the lake, into which they fall and are distributed by wave 

 and current action. The small drainage channels that cut down the long, 

 gentle slopes of the basin have been very important features in bringing the 

 plants of the upper slopes to the emersed zones around the lake. 



The recent emergence of two small islands which were submerged for nearly 

 a year will give an opportunity for a more distinctive test of the various fac- 

 tors in dissemination, including the activities of birds and other animals. No 

 such effects are yet to be seen. It is proposed to follow the history of these 

 islands somewhat closely, as no such opportunity for the observation of the 

 course of vegetation on an isolated bare area, since the destruction of the 

 plants on the island Krakatoa in the Indian Ocean in 1883, has been presented. 

 In the latter instance it was possible for the observers to visit the island only 

 at intervals of several years and no opportunity was had to make an analysis 

 of the processes involved. 



The observations on the Salton Sea have so far been carried on by means 

 of a small sailboat and a sectional steel rowboat capable of being easily carried 

 overland to convenient points around the shore. It will soon be necessary to 

 add a houseboat or floating laboratory, by means of which workers may carry 

 on observations more efficiently three or four months in the year. 



ACCLIMATIZATION: THE INDUCTIVE INFLUENCE OF PHYSICAL 

 FACTORS ON VEGETATION. 



The plantations as described in the report for 1907 have been maintained, 

 and in addition a duplicate plantation has been established in the dry mid- 

 mountain belt in Soldier Canyon, at the eastern end of the Santa Catalina 

 Mountains. The measurement of the various climatic factors at these stations 

 is being carried out, those nearest the Desert Laboratory having received the 

 most attention so far. The range of conditions embraced in these stations 

 runs from a season of about a hundred days (the time between the occurrence 

 of the last freezing temperature, early in June, to a recurrence in Septem- 

 ber) at the alpine plantation, down to the Desert Laboratory, where the air is 

 not below the freezing point more than 10 hours in a year. The intensity of 

 the insolation must vary in a large degree among the different plantations, al- 

 though not yet measured or estimated. The precipitation at the Desert Lab- 

 oratory has an average of about 12 inches yearly, while that of the alpine 

 station can not be less than 30 inches. The evaporating power of the air as 

 determined by atmometers during the vegetative season of the alpine planta- 

 tions, is about two and a half times greater at the Desert Laboratory, while for 

 the year the total at this station must be ten times that of the high plantation. 

 The total heat exposure at the Desert Laboratory for a year has been esti- 



