de;partme;nt of botanical research. 59 



was made by Professor Spalding. All plants submerged or partly submerged, 

 or included within the moist zone fringing the shore, were found to have 

 been killed, with the exception of Allenrolfia and some specimens of poplar. 

 Ten months after the maximum level of the lake had been reached and 

 subsidence had begun, the level had been lowered by 2 or 3 feet, and the 

 strip of saline shore left bare had not been occupied by plants. 



A depressed basin in the southwestern portion of the Colorado Delta was 

 explored by the expedition from the Laboratory in P'ebruary. Flood-water 

 finds its way into the Pattie Basin, nearly every year forming the Laguna 

 Maquata, which oscillates between a maximum level and almost complete dry- 

 ness with much greater frequency than the Salton Sea or Lake, offering 

 invaluable opportunities for comparative observations at a time when the 

 Department is prepared to deal with the problems involved in a thorough 

 manner. 



ACCLIMATIZATION: INDUCTIVE INFLUENCE OF PHYSICAL FACTORS 



ON VEGETATION. 



The plantations for experimental tests on problems of acclimatization have 

 been extended and modified in such manner that the following facilities are 

 now available: 



(i) The glass-house, terraces, and inclosed garden, at an elevation of 

 2,700 feet, in the domain of the Desert Laboratory on Tum.amoc Hill. 



(2) An inclosure on a small irrigated farm at 2,200 feet, near Tumamoc 

 Hill, the use of which is donated. 



(3) The austral plantation, which has been removed from Castle Rock to 

 a suitable locality at 6,100 feet, near Apache Spring, on the Sabina trail to 

 the alpine plantation on the Santa Catalina Mountains. 



(4) The alpine plantation, including about 10 acres in Marshall Gulch at 

 8,000 feet, south of Mount Lemmon and with a northerly exposure. The 

 precipitation is much greater at this station than at the others, where the 

 average is about 12 inches annually. A series of introductions and exchanges 

 is being carried on in these plantations, With marked results in the way of 

 structural changes exhibited by the plants used. Attention is being given 

 to the determination as to whether such impress is confined to the soma of 

 the plant and is non-inheritable, or whether it may be transmitted to suc- 

 cessive generations which might be grown in localities other than the one in 

 which the changes originated. 



In the measurement of the factors which make up climate a method has been 

 formulated for calculating the thermal exposure of a locality and of the 

 thermal constant of a plant with respect to the various stages of its develop- 

 ment. These quantities are quickly obtainable by calculating the area in- 

 closed by a thermographic tracing and the b^se line of freezing-point of 

 water on the record sheet, and represent hour-degrees of exposure. By this 

 method a meadow was found to receive 78,836 hour-degree units of heat in 



