THE PHYSIOLOGIC ASPECT OF THE SPECIES 

 QUESTION 



PROFESSOR J. C. ARTHUR 

 Purdue University 



Not being sure of what ground might already be 

 covered by the speakers who have preceded me on the 

 program, I take the liberty of presenting my matter 

 after giving thought to what lias been said; and I find in 

 mentally reviewing this— that the species concept as 

 presented by the previous speakers does not embrace the 

 whole field as it is forced upon me in my every day work. 

 I am especially surprised at this, because the first speaker, 

 under whom I secured my elementary training in botany, 

 is very particular in giving instruction to his pupils to 

 begin with the one-cell plant and to work up from the 

 simple to the complex. Yet, so far as I could ascertain 

 in listening most carefully, he has not now taken into con- 

 sideration a single one of the simple plants of which he 

 knows there are many thousand times as many as there 

 are of flowering plants, therefore I seem to be left some- 

 what adrift for my presentation. 



I will not attempt to give any historical aspect of the 

 question, but to take it up from the point in which it 

 appeals to me in my every-day work, for it is a problem 

 that I have been obliged to meet, and as I have met it, 

 I will present the results to you. 



As I understand it, we are taking up the question of 

 the species concept. I thought it quite well worth while, 

 in looking up the matter, to see what a man who has en- 

 tirely changed the aspect of the subject within not so 

 very many years might say as to what he considered a 

 species concept, and so I very carefully again looked 

 through my copy of Darwin's "Origin of Species." If 



