MEMORIAL OF CHARLES A. DAVIS 27 



leaving salients of scientific attack to be occupied and widened by others. 

 As always, the ever broadening area of his knowledge was bounded by an 

 ever larger circle of problems awaiting solution. 



His recognition of the different methods of bog filling has modified the 

 older conceptions. 



We have referred to the peat-bogs in the letters already cited. Here 

 are others that show his methods of work : 



"Ann Arbor, Michigan, July 14, 1903. 



"I have been out around Ann Arbor into the bogs and lakes almost continu- 

 ously since the middle of June, and am beginning to see that the peat question 

 is reallj^ an interesting scientific problem — rather a bigger and more compli- 

 cated one than that involved in the marl. It is not, however, to be solved by 

 studying the old peat-bogs, if I see the situation correctly, for the work is 

 done when the stage which we call a peat-bog is reached ; at least, here in this 

 region that is true, and the plants which are found growing in the bogs are 

 simply transient and ever changing population, moving on and off in a pretty 

 well defined order and from easily demonstrable causes. My plan of work so 

 far has been as follows : 



"(1) To visit all the bogs which Allen has examined to see what the condi- 

 tions on these were. 



"(2) To visit and study different types of bogs in various types of surface 

 configuration in this vicinity, such as the drainage channel bog, the till plain 

 bog, and the morainal bog. 



"(3) To examine carefully the numerous lakes in the district about Ann 

 Arbor to see if there was any difference in their rate of filling, in the plants 

 about them, and if there was any easily discovered relation between any set 

 of plants and the rate of filling. 



"(4) To list the plants in all the localities visited to see if in the end the 

 conclusions would be borne out by the plants themselves — that is, to sec if 

 these heterogeneously collected lists would arrange themselves into classes. 



"I think I could even now give a pretty close approximation to the true situ- 

 ation in regard to peat beds as they are made here, and could show conclu- 

 sively that the talk about sphagnum peat and other kinds of peat is based on a 

 misunderstanding, but I want more data before coming out with any such state- 

 ments, of course. It must be understood, too, that my conclusions now form- 

 ing are based on studies made here at about the southern limit of peat-bogs. 



"In regard to the Tuscola report, I am all through with the contour map, 

 thank the Lord !" 



"Ann Arbor, Michigan, December 5, 1904. 



"In regard to the poison theory, I am not at all sure that there is much of 

 any basis for it, except that in some European bogs the waters have been 

 found to be acid, and the soils also more or less so, from excess of the humic 

 acids; but the amount of such poison, if poison it is, must be exceedingly 

 variable in the soil zone in which the roots of the plants lie, and there must be 

 periods of considerable length, when rains occur so frequently during the rainy 

 growing seasons, that there is practically no excess of acid of any sort present, 



