58 REPORTS OF INVESTIGATIONS AND PROJECTS. 



mated to be 325,385 hour-degree Fahrenheit units, while that of the alpine 

 plantation can not be more than one-fifth this amount. Exact series of meas- 

 urements of all of these factors during two or three seasons will be necessary 

 at all of the plantations in the furtherance of this work. 



About 20 species from near sea-level on the Atlantic coast are now estab- 

 lished in stations at various levels, some having been brought in from southern 

 Mexico, while a number of local forms are exchanged among the various plan- 

 tations. It is worthy of record that among the introduced and exchanged 

 species are several which have proved capable of enduring the range of cli- 

 matic conditions furnished by differences of a vertical mile in elevation. 



During the present year, three solanums from southern Mexico have been 

 added to the experimental material, these plants being food-plants for the 

 beetles (Leptinotars^e) from the same region, being grown at the Desert Lab- 

 oratory by Prof. W. L. Tower, in his study of the influence of climate on 

 heredity and evolution. (See p. 69 for a fuller account.) The response of 

 the plants and, of the beetles taken together may be expected to furnish some 

 important results, and the facts already at hand seem to warrant the extension 

 of this part of the experiment in every possible way. 



The greatest value of acclimatization cultures is not to be realized by obtain- 

 ing simple records of apparent changes in organisms, such as have chiefly 

 been derived from the few systematic experiments which have been previously 

 carried out elsewhere, but rather in exact estimations of the responses of 

 plants or animals in alterations of form, structure, and functional performance 

 with relation to measured environmental factors. Five problems or groups 

 of questions have already been taken up in this manner. 



( 1 ) The climatic experiments of Professor Tower already mentioned. 



(2) A study of the influence of climates on heredity of lineal series of 

 plants introduced and exchanged. Seeds of the second generation of some 

 species are now on hand and may be tested in the new locality or original 

 habitat. 



(3) An exact determination of the part climatic factors may play in trans- 

 mission and dominance of characters in hybridization. Three pairs of species 

 are now in cultivation and reciprocal crosses are being made at various eleva- 

 tions in order to ascertain the possible influence of climate, both on the com- 

 position of the offspring and on the factors governing survival. 



(4) Comparative cultures are being made of forms which pass as closely 

 related species growing at different altitudes under different combinations of 

 climatic factors. 



(5) The structure and performance of foliar organs under divergent cli- 

 matic conditions. The different structures exhibited by leaves of individuals 

 of a species at 8,000 feet and others at 2,600 feet are being made out, and 

 an attempt is being made to interpret these with regard to their physio- 



