126 PLANT PHYSIOLOGY 



reason or another, merit emphasis. In general, the problems in plant 

 physiology have been well brought out and systematized through 

 the monumental work recently completed by Professor Pfeffer. To 

 him the science owes a debt of gratitude which may be acknowledged 

 as well by one who attempts to suggest future work as by the his- 

 torian. Again, due recognition should be made of those who have 

 in recent years based upon this or any similar topic valedictory 

 addresses before various botanical organizations, notably, those 

 of Professors Vines, Ward, Barnes, Reynolds Green, and others. 



The fact that every cell or organ requires its food materials, or at 

 least its nutrients, in liquid form, readily emphasizes the funda- 

 mental importance of those problems suggested by the relation of 

 the plant to solutions. The mechanisms for absorption and the general 

 and special diosmotic properties of the living cell, all of which have 

 been studied with the most consummate skill, have yielded matchless 

 results, yet the rewards for future research show at present no dis- 

 tinct limitations. It has not been possible to determine the nature 

 of the plasmatic membrane which directly or indirectly possesses 

 such marked powers of selection and accumulation. The conditions 

 under which the activities of this membrane may be modified are 

 but poorly understood; and it is, perhaps, quite beyond the present 

 possibilities to determine the mechanism of this modification, for 

 in that must be involved one of the most important vital activities 

 of protoplasm. Perhaps when many more data have been accumu- 

 lated by a study of plants of diverse habitat, the conditions of this 

 modification may be more clearly distinguished. It is known that 

 continued endosmosis of a particular solute depends largely upon 

 the use or transformation of this solute within, yet it is not always 

 possible to demonstrate any change in the substance absorbed. In 

 any event, it is necessary to ask further light upon the exosmotic 

 resistance of the plasmatic membrane to the accumulation of turgor- 

 producing substances, or, in other words, to a further explanation 

 of what may' be termed one-way penetration. To these phenomena 

 the processes of excretion and secretion are closely allied, whether 

 they are ultimately, periodically, or continuously the function of cer- 

 tain protoplasts. 



Further chemical knowledge is needed dealing with the meaning 

 of high pressures and of the accommodation of very high pressures 

 in the fungi. As a rule, those protoplasts seem to be resistant to 

 such high pressures which are also resistant to cold, desiccation, and 

 other stimulation. Mayerburg, working* under the instruction of 

 Professor Pfeffer, has recently applied himself to a study of the 

 method by means of which the organism may regulate its turgor. 

 It is evident that one of two propositions must be assumed, and that 

 increased turgor may be produced either (1) by the penetration 



