150 
| NATURE 
[FEBRUARY 3, 1923 

thermal oscillation, or adsorption, or many other 
causes, it may in addition exert an impulse on the 
molecule in the direction ob, receiving the equal and 
opposite impulse along oa, or it may exert an impulse 
along oa, receiving one along ob. Should the former 
lateral effect predominate, the directing effect of the 
cone will be increased; should the latter predominate 
the effect will be reduced, but there is no reason to 
suppose that, in any representative period of time, 
either will predominate over the other. 
ARTHUR FAIRBOURNE. 
King’s College, University of London, 
Strand, W.C.2., 
January I. 

Sir Isaac Bayley Balfour. 
Att botanists and lovers of flowers will mourn the 
death of the Edinburgh professor, who served science. 
and horticulture as few men have ever done. The 
occasion seems opportune to relate an incident 
comparatively unimportant in itself but in a manner 
typical. Many years ago a beautiful Primula, called 
by Greene P. vusbyi, was discovered in the Mogollon 
Mountains of New Mexico. Later, in the Sandia 
Mountains of the same State, one of my students found 
an apparently distinct species, which I named 
P. ellisi@. These primroses occupied distinct and 
isolated mountain ranges, but were so similar, at 
least in the herbarium, that a German writer pro- 
nounced them identical. No one, so far as could be 
learned, had seen more than one of them alive, and it 
was the living plants we needed to settle the matter. 
I was able to procure seeds of P. ellisie for Prof. 
Bayley Balfour, and in 1921, when my wife and I 
visited him in Edinburgh, he not only had ellisie in 
full flower, but also vusbyi, the seeds of which he had 
secured from some other collector. It was a dramatic 
moment when the Professor held the two pots, one in 
each hand, and pointed out that the plants were quite 
distinct. Thus, in Edinburgh, we learned a lesson in 
New Mexico botany, which we had never been able 
to learn when resident for years in that region. No 
doubt others could relate parallel experiences. 
T. D. A. COCKERELL. 
University of Colorado. 

Age and Area in Natural Selection. 
THE account in Nature (December 2, vol. IIo, 
Pp. 751) of the discussion at Hull on ‘‘ The Present 
Position of Darwinism ”’ has interested me greatly. 
Of course I realise that such an account must be 
summary and omit much that is said, but I am struck 
by the fact that apparently none of the speakers 
mentioned what seem to me two fundamental and 
even fatal objections to the Age and Area hypothesis 
as a subject for the theory of Natural Selection. 
In the first place, the fact that “‘ genus ”’ is a very 
inexact term, largely dependent on the “ personal 
equation,’’ seems to be completely overlooked. Some 
of us tend to large genera, some to small. In his 
article in the Nineteenth Century, Dr. Willis refers to 
a genus of more than 1500 species, In my opinion, 
to call such a group a genus is positively grotesque ; 
it includes probably scores of what I would call 
genera. I can juggle the genera of echinoderms (my 
own special group) so as to lend apparent support to 
the Age and Area hypothesis, or I can re-define them 
so as to contradict it strongly, and in either case I 
can quote high authorities or give excellent reasons 
for my course. 
In the second place, the Age and Area hypothesis 
really explains nothing. It merely restates in a more 
or less tabular way what every taxonomist, who has 
NO. 2779, VOL. 111] 


given any attention to distribution, knows is often 
the case. I say “‘ often’’ because, as some of those 
who took part in the discussion at Hull pointed out, 
there are many cases of distribution which do not 
fall in with this tabulated arrangement. No causal 
connexion between age and area is brought out in 
the proposed hypothesis. The only causal factors 
suggested are time and an inherent tendency to 
diversification, and surely both of these are given 
abundant play in the theory of Natural Selection. . 
I note with interest, perhaps I might say amuse- 
ment, the statement by Mr. Cunningham that Natural 
Selection is ‘‘ as extinct as the dodo.’”’ It may be in 
the land of its birth, but it is still very much in 
evidence in America. Nearly every systematic 
zoologist whom I know personally believes in it asa — 
factor in evolution, though the importance attributed 
to it may vary greatly. Prof. E. G. Conklin of — 
Princeton, certainly one of our foremost zoological — 
thinkers, has just completed a course of Lowell 
Institute lectures in Boston on “‘ The Revolt against 
Darwinism,’ in which he has most clearly and 
emphatically stated his strong conviction, not only 
that such revolt is unjustifiable, but that Natural 
Selection is the most important theory that has yet 
been proposed for helping us to understand adapta- 
tion. It surely seems a little rash to call Natural 
Selection, or anything else, “‘ extinct ’’ because it has 
disappeared from one’s own horizon. Horizons con- 
tract with increasing near-sightedness. 
HUBERT LYMAN CLARK. 
Cambridge, Mass., U.S.A., 
December 22, 1922. 

The Cause of Anticyclones. — 
May I be allowed to suggest that the region of an ~ 
anticyclone finds its most likely interpretation as an 
area hemmed in by cyclone systems. I agree with 
Mr. Dines (NATURE, December 23, vol. 110, p. 845) 
that it is the mass of air over the area that is important. 
It is a matter of personal observation that, as Mr. 
Dines says, “ the steady and persistently high baro- 
metric pressure that has prevailed over southern — 
England during most of the autumn’”’ has been 
associated with the overlapping high overhead here 
of the margins of cyclone systems that were simul- 
taneously from west to eastwards on our north and 
on our south respectively. The phenomenon of 
contrary currents at high elevation is an inseparable — 
feature, in my experience, of anticyclonic conditions. — 
May it not be a conditional factor of these anti-— 
cyclonic high pressure areas (?) the “‘mass”’ of air 
being piled to excess and held in situ by the con- 
flicting winds of over-reaching cyclone lips. The 
play of antagonistic forces of movement and of their 
accompanying contrasts of humidity and temperature 
may be answerable for all other anomalies of anti- 
cyclone areas. What are wanted are observations of 
winds of highest elevation, which are only to be 
obtained by the method of employing a projected — 
telescopic image of the sun, which renders visible and — 
legible the ‘‘ wind-billows’”’ of individual strata of 
movement, CATHARINE O, STEVENS. 
The Plain, Boar’s Hill, Oxford, 
January 16. 

The Name of the Pond Snail. 
In Nature for January 13, p. 49, two writers of 
authority call this snail Limn@a peregra. The word 
““peregra ’’ is not Latin—a fact which at one time 
had penetrated to the consciousness of most concho- 
logists and malacologists but appears to have been 
again forgotten. FL Av B, 


