6 NATURE 
[Marcu 7, 1912 
beginning with the seed and germination. Dr. 
Cavers lays some stress on the second chapter, 
which is intended to impress a more thorough 
knowledge of the organic products in plants. 
Seeing that the real aim of students’ courses is 
rather to teach general methods and provide train- 
ing than to implant facts, tests for proteins and 
other complex substances are much less valuable 
than the more tangible experiments of a physical 
nature. : 
Except in this matter, there is no hesitation in 
recognising that the author presents a remarkably 
clear and informative series of experiments. There 
is always satisfaction in experiments requiring 
simple and natural material, as in the test of a 
living turnip with beetroot juice, but Dr. Cavers 
on the whole favours the view that there is a neces- 
sity for specially designed apparatus capable of 
yielding exact measurements, in which connection 
he directs attention to several instruments de- 
signed by Prof. Ganong. An appreciable amount 
of generally unknown detail is supplied in the life- 
history of Pellia and Funaria, and otherwise this 
section is no mere repetition of available informa- 
tion. Teachers will be well advised to consult the 
book before drafting their physiological courses, | 
as they are tolerably certain to discover sugges- 
tions or new experiments. 
IBJFIEIMDIES INO) IED IBID ONES, 
[The Editor does not hold himself responsible for 
opinions expressed by his correspondents. Neither 
can he undertake to return, or to correspond with 
the writers of, rejected manuscripts intended for 
this or any other part of Nature. No notice is 
taken of anonymous communications. ] 
Heredity. 
So long as naturalists persist in using ill-defined 
terms, the meaning of which they have not clearly 
thought out, the controversy about the inheritance of 
so-called ‘‘ acquired characters ’’ is bound to be sterile 
and interminable. If it be once granted that 
organisms are the product of the interaction of two 
sets of factors—the factors of the inheritance and the 
factors of the environment—it becomes obvious that 
not only every organism, but every ‘“‘ character’ of 
an organism, must be the result of both sets of 
factors. And if by ‘‘ character’? we mean any such 
resulting structure or property as it appears ‘to our 
senses, as we see it before us, then it becomes mani- 
fest that no character can be due wholly to inherit- 
ance or wholly to environment. The very words 
*“acquired character ’’ involve a fatal fallacy—sug- 
gesting as they do that one character may be more 
acquired than another. Since such wholly acquired 
characters do not exist, it is waste of time to discuss 
their possible inheritance. 
Even Dr. Reid, in his letter in last weelx’s NATURE, 
does not entirely escape from this logical error when 
he uses the word inheritance for the transmission of 
acquirements (characters) in unicellular organisms. 
It is a return to the vague, popular use of the term 
which would inevitably lead us back into the old 
tangle of inconsistencies. The biologist may define 
inheritance as the transmission of hereditary factors 
—it is not ready-made characters which are inherited, 
but the factors which help to produce them. The 
transmission in a protozoon of the characters of its 
parent is no more inheritance in the strict biological 
NO. 2210, VOL. 89] 
sense than is the transmission of the eggshell and 
albumen from the fowl to the chick, or of money from 
father to son. 
Variation may be caused by changes in the environ- 
ment giving rise to ‘‘ modification,’’ or by changes in 
| the inheritance (the totality of the hereditary factors). 
“ 
giving rise.to ‘‘ mutation.’’ Changes in the inherit- 
ance are due to the rearrangement of, addition to, or 
subtraction from the factors of inheritance. Ulti- 
mately these changes must be referred to the environ- 
ment, and it is only when something from the 
environment thus alters or enters into the inheritance 
that mutation can occur. 
-It follows that if certain observations seem to show 
that ‘‘ acquired characters’’ are transmitted by true 
inheritance, either they must be capable of some other 
interpretation, or our premise that every organism is 
the resultant of two sets of factors must be wrong. 
No escape from this alternative seems possible. ~ 
The dogmatic tone of this letter will, I hope, be 
forgiven me, as it has been assumed merely for the 
sake of brevity. E. S. Goopricnu. 
Merton College, Oxford, March 1. 
Mars and a Lunar Atmosphere. 
In Narure, February 22, p. 565, reference is made 
to an interesting observation by Prof. Luther, of the 
Diisseldorf Observatory. The note states that he 
saw the half of the disc of Mars nearest the moon 
become green just before occultation on December 4, 
1911, and he suggests that this may have been due 
to a lunar atmosphere. The time was 16h. 4om. 
(Greenwich mean time), and I notice that the moon 
was full at 14h. 52m. on December 5, so that, at the 
time of the observation, the unilluminated crescent of 
the moon towards the planet must have been ex- 
tremely narrow, so that the illuminated part of the 
lunar disc must have been quite close to the planet. 
Now no refracting telescope is perfectly achromatic, 
and as one of the residual colours is green, it seems 
to me possible that this colour may have been due to 
moonlight imperfectly achromatised. It may also be 
suggested that the reddish colour of Mars might lead 
to the focus of the telescope being different for the 
planet and the moon. Another suggestion is that the 
colour of the planet might give rise to a complemen- 
tary tint. 
Turning to the date of Prof. Luther’s previous ob- 
servation, October 16, 1902, I find that the moon was 
full on that very day, and this seemed to link the 
two observations together, hoth being associated with 
a nearly full moon. 
But, to my surprise, I found, on consulting the 
Nautical Almanac table of occultations, that no occul- 
tation of Mars, or of any planet, is set down for 
October 16, 1902, and, on looking up the positions of 
the moon and of Mars, it is obvious that none could 
have occurred, as they were distant in R.A. by some 
nine hours. It is evident then that there is some 
mistalxe in the earlier date, unless it is meant to apply 
to some small stars in Pisces. 
I observed with a refractor the disappearance 
occultation of Mars at the dark limb of a moon 
rather more than half-full in the early morning of 
January 29 this year, but saw no trace of any green 
colour on the disc of the planet. 
C. T. WHItMELt. 
Hyde Park, Leeds, February 26. 
The Teaching of Mathematics. 
IN un article entitled ‘‘The Teaching of Mathe- 
matics’ in Nature of November 30, 1911, considerable 
space is devoted to a memorandum written by me for 
ie 
