Makrcu 8, 1901.] 
slopes become xerophytic. In the valley 
itself a flood plain eventually develops 
which has at first a hydrophytic and finally 
amesophytic flora. There are local digres- 
sions from this history, but in general it 
may be said that mesophytic flood plain 
vegetation is ever on the increase and may 
be regarded as the ultimate type. 
Base-leveling and its Faunal Significance, with 
Illustrations from Southeastern United States : 
CHaries C. ADAMS. 
Attention was called to the necessity of 
correlating the influences of the base-level- 
ing processes with the distribution of hab- 
itats, and especially the importance of a 
knowledge of river histories in the study of 
fresh-water faunas. An outline was given 
to illustrate the principles involved in the 
reduction of an elevated country to sea- 
level. By the growth of valleys there is a 
decrease of uplands, a premium being 
placed upon those forms whose habitat is 
increasing in area; thus tension lines are 
produced. There is a definite succession of 
forms advancing up a valley, and thus in 
descending a river one may find a rough re- 
capitulation of the types of faunas which 
occupy a stream during its ideal history. 
With a reduction of divides, rapid water, 
upland faunas are the first tomix. Atten- 
tion was attracted to the importance of the 
base-leveling factors about two years ago, 
in connection with the studies on the Pleu- 
roceride. The anomalous distribution of 
this family in the Tennessee and Coosa- 
Alabama river systems was at once ex- 
plained upon learning, at that time, that 
formerly the Tennessee river from Chatta- 
nooga flowed to the Gulf via the Coosa- 
Alabama system. Valley faunas are isolated 
by uplands and vice versa. The Cumber- 
land Plateau and the Smoky Mountains 
have been isolated by the Tennessee valley 
and consequently have peculiarities in their 
fauna. The land shells, according to Pils- 
SCIENCE. 
373 
bry, of the Cumberland Plateau have about 
20 characteristic species or varieties and the 
Smoky Mountains about 25. The geologists 
(Woodworth) have had a better apprecia- 
tion of these factors. Students of distribu- 
tion should give more importance to habitat 
as a dynamical factor in their study of 
faunal problems. This will lead to the 
study of faunas in a comparative and ge- 
netic way. 
Demonstration of certain Features in the Re- 
actions of Infusoria: H. S. JENNINGS. 
Demonstrations by means of the project- 
ting microscope and stereopticon, of the re- 
actions of unicellular organisms toward car- 
bon dioxide and various other chemicals. 
The demonstrations were essentially the 
same as those described in Screncer for Jan- 
uary 11, 1901, pp. 74, 75. 
On certain Methods by which Organisms Reg- 
ulate their Movements with Relation to the 
Position of External Objects acting as Stim- 
wi: H.S. Jenninas and RayMonD PEARL. 
The paper showed the biological sig- 
nifieance of the revolution on the long axis, 
with the resulting spiral path, which is a 
feature of the swimming of many lower 
organisms. These organisms usually tend 
to swerve toward one side, and thus to swim 
in circles; the revolution on the long axis 
converts this circular path into a spiral one, 
and thus permits an unsymmetrical organ- 
ism to follow a course which is in effect a 
straight one. The paper gave an account 
of very simple mechanisms for turning to 
or from a source of stimulus in a number 
of organisms, Rotifera, ctenophores, flat- 
worms, and the earthworm. 
Experiments in Artificial Parthenogenesis: J. 
Lore. Already described in Scrence. 
Cenogametes: Dr. B. M. Davis. 
The peculiar multinucleate gametes of 
the Phycomycetes were considered and the 
results of Dr. Stevens’ studies and the 
writer’s on Albugo were described. These 
