656 Plain, Prairie, and Forest. [November, 
abrupt line can be drawn between alternation and ordinary sex- 
ual reproduction, þut that they are different forms of the same 
process. In a future paper I hope to say a few words upon 
this subject, and to show how all the strange peculiarities of Sal- 
pa receive a simple explanation upon the theory that it is the 
descendant of an ordinary tunicate which has been modified by 
natural selection. 
PLAIN, PRAIRIE, AND FOREST. 
BY PROF. J. D. WHITNEY. 
PART I 
i more the prairies are studied, the less will one feel dis- 
posed to adopt any theory for their origin dependent on cli- 
mate, and the more will the attention be turned to the question 
of the character of the soil, the distribution of the geological for- 
mations from which this soil has been derived, and the cycle of 
recent geological events by which it has been distributed and ac- 
cumulated in its present position. It is evident, however, that in 
the discussion of a question of this kind full details of the obser- 
vations made cannot be given; they would occupy volumes. — It 
is for the observer himself, on carefully analyzing and classifying 
the results of his examinations, to state the conclusions at which 
he has arrived ; a catalogue of the localities visited would be of 
little service to any one else in enabling him to form an inde- 
pendent opinion. 3 
As the result of a great number of observations made over all 
the prairie States, we find, almost without exception, that absence 
of forests is connected with extreme fineness of soil, and that 
this fine material usually occurs in heavy deposits. It seems 
hardly necessary to enlarge on the characteristics of the so-called 
“prairie soil.” To look at a plow with which the prairie has 
been broken up ought to be a sufficient indication of this fine- 
ness. How often has the writer admired the beautiful polish put 
upon this common utensil used on the western prairies, and "E 
trasted its appearance with that of the scratched and battere 
article with which the hills of New England had been belabored. 
Let us, however, quote a few paragraphs illustrative of the nature 
of the prairie soil from some of the Geological Survey Reports, 
beginning with that of Illinois. f the 
“ All the part of the county [Boone, Illinois] south 0 s 
Kishwaukee may be called a treeless prairie, characterized PY 
