182 BOTANICAL GAZETTE S [MARCH 
short that exact study year by year at a given point makes it possible 
to determine not only the trend of succession, but the exact way in 
which it comes about. We can see one stage replacing another 
before our eyes, and hence we may hope some day, if we exercise 
sufficient ingenuity and patience, to understand the underlying 
causes of the change. It is clear therefore that vegetative cycles 
are not of equal value. Each climatic cycle has its vegetative 
cycle; each erosive cycle within the climatic cycle in turn has its 
vegetative cycle; and biotic factors institute other cycles, quite in- 
dependently of climatic or topographic change. It is small wonder 
that within this complex of cycle within cycle, each moving inde- 
pendently of the others and at times in different directions, 
dynamic plant geography has accomplished so little in unraveling 
the mysteries of succession. It may be some small contribution to 
this end, if the preceding considerations assist in delimiting the 
problems. 
THe UNIVERsiTy or CHICAGO 
LITERATURE CITED 
1. Kivc, Wixi1am, Of the bogs and loughs of Ireland. Phil. Trans. Roy- 
Soc, London 15§:948-960. 1685. 
- Burron, G. L. L., Mémoire sur la culture des foréts. Hist. Acad. Roy. 
Sci. Paris 1742: 233-246. 
3- Brpere, I. J., Oeconomia naturae. Amoen. Acad. 2:1-52. 1749- 
4. DUREAU DE LA Matte, A. J. C. A., Mémoire sur l’alternance ou sur Ce 
N 
b 
yt 
n 
SI 
z 
4 
si 
as 
wy 
@ 
o 
5 
() 
ch 
a 
3 
2. 
5 
. 
wm 
. 
q. 
=) 
Qu 
oO 
oi 
As 
o 
a 
od 
rot) 
Cen y 
n 
E 
i=) 
& 
3 
fa) 
an 
- Forses, Epwarp, On the distribution of endemic plants, more espe sei 
those of the British Islands, considered with regard to geological — 
Brit. Assoc. Rep. 18457:67-68. 
- VAUPELL, C., De nordsjaellandske Skovmoser. Copenhagen. wane 
- Retssex, S., Ueber die Bildungsgeschichte der Donauinseln im mittleren 
Laufe dieses Stromes. Flora 39:622-624. 1856. 
VAUPELL, C., De l’invasion du hétre dans les foréts du Danemark. an 
Sci. Nat. Bot. IV. 7:55-86. 1857. 
oon 
? 
