TRANSACTIONS OF SECTION D. 759 
their nature and source: (1) There are those variations which appear to have no 
relation to the external conditions, for they take place when these remain un- 
changed, e.g. in members of the same litter; they are inherent in the constitution 
of the individual. These we shall call constitutional variations, or, as their 
“ssn seems nearly always to be connected with reproduction, they may be 
called genetic (congenital, blastogenic) variations. (2) The second kind of’ varia- 
tions are those which are caused by the direct action of external conditions. 
These variations constitute the so-called acquired characters. 
My first object is to consider these two kinds of variations, their nature, their 
causes, and their results on subsequent generations, and to inquire whether there 
are any fundamental differences between them. In this connection it is of par- 
ticular importance that we should inquire whether acquired modifications are 
transmitted in reproduction. As is well known, there are two schools of thought 
holding directly opposite views as to this matter. The one of these schools—the 
so-called Lamarckian school—holds that they may be transmitted as such in re- 
production ; the other school, on the other hand, maintains that acquired modifi- 
cations affect only the individual concerned, and are not handed on as such in 
reproduction. ‘That the decision of the matter is not only theoretically important, 
but also practically, is evident, for upon it depends the answer to the question 
whether mental or other facilities acquired by the laborious exercise of the indi- 
vidual are ever transmitted to the offspring—whether the facility which the 
individual acquires in resisting temptation makes it any easier for the offspring to 
do the same, whether the effects of education are cumulative in successive genera- 
tions. To put the matter as Francis Galton has put it, is nature stronger than 
nurture, or nurture than nature ? 
We have then two kinds of variation to consider: (1) genetic variation, (2) 
acquired moditication. It is the formerof these—namely, genetic variation—with 
which I wish primarily to deal. Let us examine more fully the mode of its 
occurrence. 
Genetic Variation. 
Organised beings present, as you are aware, two main kinds of reproduction, 
the sexual aud the asexual. These two kinds of reproduction present certain differ- 
ences, of which the most important, and the only one which concerns us now, is 
the fact that genetic variation is essentially associated with sexual reproduc- 
tion, and is rarely, if ever, found in asexual reproduction. In other words, 
whereas the offspring resulting from asexual reproduction as a rule exactly 
resemble the parent, they are always different from the parents in sexual reproduc- 
tion. I am aware that I am treading on disputed ground. You will observe that I 
do not make the assertion that asexually produced offspring a/ways exactly resemble 
the parent, and never present genetic variations. To say that would be going too far 
in the present state of our knowledge. Therefore I have put the matter less 
strongly, and merely assert that whereas asexual reproduction is cn the whole 
characterised by identity between the offspring and the parent, sexual reproduction 
is always characterised by differences more or less marked between the two; and 
I reserve the question as to whether genetic variations are ever found in asexual 
reproduction for later consideration. 
This modified form of the statement will, I think, be admitted on all hands, but 
before going on I will illustrate my meaning by reference to actual examples. 
Asexual reproduction is a phenomenon comparatively rare in the animal king- 
‘dom, and when it does occur it is exceedingly difficult to investigate from this 
particular point of view. In the vegetable kingdom, on the other hand, it is 
quite common. All, or almost all, plants possess this power, and in a very 
great many of them the result of its exercise can be fully followed out, and con- 
trasted with that of sexual reproduction, Let us follow it out in the potato-plant. 
The potato can and does normally propagate itself asexually by means of its under- 
ground tubers. As you will know, if you take oneof these and plant it, it gives 
rise to a plant exactly resembling the parent. If the tuber (seed as it is sometimes 
erroneously called) be that of the Magnum Bonun, it gives rise to a plant with 
