422 THE AMEBIC AX NATURALIST [Vol. XLIII 



many ecologists are making use of temperature data, this 

 point will bear some emphasis. Feeling that ecology is 

 new, and exact instrumental work is the kind that counts, 

 it is very easy, when one has secured a fine series of 

 readings, or better still, a complete thermographic trac- 

 ing for a growing season, to entertain the impression that 

 he has accomplished something of note ; whereas the fact 

 in the matter simply is that if he has done his work well, 

 it is of a quality with the routine work of a weather 

 bureau. To relate the physical data to the manifold 

 activities of a living plant is another matter, and calls 

 for all the power of critical thought and all the knowledge 

 of physiology which any man can command. 



For our purpose, it seems possible to do little more 

 than to point out some difficulties to be surmounted. To 

 begin with, any method which assigns increasing values 

 to higher temperatures must go astray as soon as the 

 plant's optimum is passed, and for most of the plants we 

 are dealing with, we do not know where that is. If, also, 

 as there is some reason to believe, the growth-tempera- 

 ture curve has more than one maximum, a still further 

 difficulty would be brought in. 



Furthermore the ecologic optimum is made up of many 

 harmonic optima, and may vary in different life phases 

 of the same plant. In experiments in forcing fruit trees, 

 it has been found that the optimum for blooming is mark- 

 edly lower than for other periods for the plant's activity. 

 Finally the temperatures recorded are for the soil or air, 

 whereas the ones wanted are those that prevail within 

 the plant. Leaves and shoots are warmed by sunshine 

 and cooled by the evaporation of water. In this way tem- 

 peratures may be brought about which differ materially 

 from those recorded by a thermometer alongside. In the 

 case of an Alpine plant, sheltered in some sunny angle 

 of rock, how widely the temperature within its leaves 

 may differ from that shown by a thermometer near by, 

 properly set up for air temperatures in shade ! 



On the positive side, there seems less to be said. It 



