144 PLANT PHYSIOLOGY 



origination of species. Continuous variation must be manifest by 

 relatively slight variations; and it would be unfair to expect at 

 this time the experimental proof of its efficiency. It may even be 

 assumed that there is a complete series between continuous varia- 

 tions and discontinuous variations, as well, perhaps, as between 

 the possibilities of inheriting immediately or ultimately such varia- 

 tions. Many of the problems in plant physiology are distinctly 

 practical problems. The task of the physiologist is primarily to 

 study the activities of plants irrespective of practical bearing. To 

 have the greatest possible breadth and force, however, the culti- 

 vated plant may not be neglected in any of its artificial environmental 

 conditions. It is unfortunate that as yet physiological botany has 

 not been made fundamental to agronomy, horticulture, forestry, 

 and other sciences, arts, or commercial pursuits. Physiology can- 

 not be limited by any practical problems, nor can any sacrifices 

 be made, but a sympathy with commercial endeavor will invigorate 

 the work, will afford equipment, and will contribute towards the 

 common good. 



In conclusion, it may be said that present-day physiology, even 

 more than any other section of biological science, is fundamental. 

 Many phases of pathology, ecology, phylogeny, and experimental 

 morphology, especially, may not be clearly differentiated as sections. 

 Broadly conceived, plant physiology concerns itself: 



(1) With the relationships of existing organisms, ontogenetically 

 and phylogenetically. Phylogeny would necessarily claim much of 

 this general field, as would also morphology, ecology, and other sub- 

 divisions. 



(2) With the functions or activities of organs, tissues, and cells, 

 and the interactions and interrelations of these one \vith another 

 and with external forces. It is here that morphology touches physi- 

 ology most closely, and here experimental morphology must have 

 its basis. 



(3) With the incorporation and excretion of matter, metabolism, 

 and growth, the sources and uses of energy, irritability, and the 

 minute constitution of living matter. In this last are included many 

 of the most fundamental problems, not necessarily problems in- 

 volving the question "What is life?" but problems concerned with 

 the resolution of those factors and an intimate knowledge of those 

 materials which make life possible. 



