128 PLANT PHYSIOLOGY 



blems are not new, and in a qualitative way, at least, the problem 

 of the relationship of the conservation of moisture and the tilth of the 

 soil to productiveness has been duly appreciated by the best agro- 

 nomists. We must notice with regret, therefore, that botanists have 

 not always appreciated the importance of such work. Either directly 

 or indirectly the water factor is a chief one in regulating the activities 

 of the living plant and must be considered from every possible point 

 of view. 



It may, perhaps, be less a problem than a routine matter to de- 

 termine the relation of the rate of absorption of salts in the soil 

 solutions to water under the varying conditions of growth and 

 transpiration. Nevertheless, information of this nature is important. 



In spite of all the recent work, the physical explanation of the 

 ascent of water in. trees is a problem which must be mentioned. 

 The renewed investigations which have been made along this line 

 from an objective point of view will undoubtedly contribute to its 

 eventual solution. 



It is a matter of interest that in their studies of the physics of 

 transpiration, Brown and Escombe have found evidence to regard 

 this process also as a matter of diffusion through multiperforate 

 septa, rather than a matter of mass action. It is calculated that by 

 diffusion water may pass out of the stomates to an extent as much 

 as six times the actual amount of transpiration which has been 

 observed in special cases. 



The great number of cytological investigations which have been 

 completed within the past ten years indicate notable advancements 

 in a most important field; and this is particularly true with rela- 

 tion to the study of nuclear phenomena. Through this work light 

 has been thrown upon many problems of cell physiology and of 

 development: and as a result of the latter new theories of heredity 

 have been advanced. Nevertheless, the field for investigation has 

 been constantly broadened and many new lines of research made 

 possible. In spite of the excellent results accomplished, there is yet 

 great uncertainty as to the interpretations which have frequently 

 been made. In no field of work, perhaps, is it possible for the per- 

 sonal factor to enter into the results more largely than in this. 

 Again, it is unfortunately true that fixed material has been studied 

 almost to the exclusion of all other and that even general observa- 

 tions relating to the conditions of growth have been omitted in 

 many instances. Much attention has been bestowed upon the min- 

 utest details which seem to be of morphological significance in the 

 nucleus; but 'often the purely physiological side has been insuffi- 

 ciently emphasized. It is quite possible that in different plants 

 the exact method of chromosome division, or the manner of nucleo- 

 lar disappearance, may not be similar; and it is certainly well 



