October 11, 1888. ] 
JOURNAL OF HORTICULTURE AND COTTAGE GARDENER. 
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about. Heredity explains the resemblance ; Mr. Darwin’s great dis¬ 
covery was that variation worked upon by natural selection explained 
the difference. That explanation seems to me to gather strength every 
day, and to continually reveal itself as a more and more efficient solvent 
of the problems which present themselves to the student of natural 
history. At the same time, I am far from claiming for it the authority 
of a scientific creed, or even the degree of certainty which is possessed 
by some of the laws of astronomy. I only affirm that as a theory it has 
proved itself a potent and invaluable instrument of research. It is an 
immensely valuable induction ; but it has not yet reached such a posi¬ 
tion of certitude as has been attained by the law of gravitation ; and I 
have myself, in the field of botany, felt bound to protest against con¬ 
clusions being drawn deductively from it without being subjected to the 
test of experimental verification. This attitude of mine, which I 
believe I share with most naturalists, must not, however, be mistaken 
for one of doubt. Of doubt as to the validity of Mr. Darwin’s views I 
have none : I shall continue to have none till I come across facts which 
suggest doubt. But that is a different position from one of absolute 
certitude. It is therefore without any dissatisfaction that I observe that 
many competent persons have, while accepting Mr. Darwin’s theory, 
set themselves to criticise various parts of it. But I must confess that 
I am disposed to share the opinion expressed by Mr. Huxley, that 
these criticisms really rest on a want of a thorough comprehension. 
Mr. Komanes has put forward a view which deserves the attention 
due to the speculations of a man of singular subtlety and dialectic skill. 
He has startled us with the paradox that Mr. Darwin did not, after all, 
put forth, as I conceive it was his own impression he did, a theory of the 
origin of species, but only of adaptations. And inasmuch as Mr. 
Romanes is of opinion that specific differences are not adaptive, while 
those of genera are, it follows that Mr. Darwin only really accounted 
for the origin of the latter, while for an explanation of the former we 
must look to Mr. Romanes himself. For my part, however, I am alto¬ 
gether unable to accept the premises, and therefore fail to reach the 
conclusion. Specific differences, as we find them in plants, are for the 
most part indubitably adaptive, while the distinctive characters of 
genera and of higher groups are rarely so. Let anyone take the 
numerous species of some well-characterised English genus—for ex¬ 
ample, Ranunculus ; he will find that one species is distinguished by 
having creeping stems, one by a tuberous root, one by floating leaves, 
another by drawn-out submerged ones, and so cn. But each possesses 
those common characters which enables the botanist almost at a glance, 
notwithstanding the adaptive disguise, to refer them to the common genus 
Ranunculus. It seems to me quite easy to see, in fact, why specific 
characters should be usually adaptive, and generic not so. Species of 
any large genus must, from the nature of things, find themselves ex¬ 
posed to anything rather than uniform conditions. They must acquire, 
therefore, as the very condition of their existence, those adaptive 
characters which the necessities of their life demand. But this rarely 
affects those marks of affinityiwhich still indicate their original common 
origin. No doubt these were themselves once adaptive, but they have 
long been overlaid by newer and more urgent modifications. Still, 
Nature is ever conservative, and these reminiscences of a bygone history 
persist; significant to the systematic botanist as telling an unmistakeable 
family story, but far removed from the stress of a struggle in which 
they no longer are called upon to bear their part. 
Another episode in the Darwinian theory'is, however, likely to occupy 
our attention for some time to come. The biological world now looks 
to Prof. Weismann as occupying the most prominent position in the 
field of speculation. His theory of the continuity of the germ-plasm 
has been put before English readers with extreme lucidity by Prof. 
Moseley. That theory, I am free to confess, I do not find it easy to 
grasp clearly in all its concrete details. At any rate, my own studies do 
not furnish me with sufficient data for criticising them in any adequate 
way. It is, however, bound up with another theory—the non-in¬ 
heritance of acquired characters—which is more open to general dis¬ 
cussion. If with Weismann we accept this principle, it cannot be 
doubted that the burden thrown on natural selection is enormously in¬ 
creased. But I do not see that the theory of natural selection itself is 
in any way impaired in consequence. 
The question, however, is, Are vre to accept the principle ? It ap¬ 
pears to me that it is entirely a matter of evidence. It is proverbially 
difficult to prove a negative. In the analogous case of the inheritance 
of accidental mutilations, Mr. Darwin contents himself with observing 
that we should he “cautious in denying it.” Still, I believe that, 
though a great deal of pains has been devoted to the matter, there is no 
case in which it has been satisfactorily proved that a character acquired 
by an organism has been transmitted to its descendants ; and there is, 
of course, an enormous bulk of evidence the other way. 
The consideration of this point has given rise to what has been called 
the new Lamarckism. Now, Lamarck accounted for the evolution of 
organic Nature by two principles—the tendency to progressive ad¬ 
vancement and the force of external circumstances. The first of these 
principles appears to me, like Nageli’s internal modifying force, to be 
simply substituting a name for a thing. Lamarck, like many other 
people before him, thought that the higher organisms were derived from 
others lower in the scale, and he explained this by saying that they had 
a tendency to be so derived. This appears to me much as if we ex¬ 
plained the movement of a train from London to Bath by attributing it 
to a tendency to locomotion. Mr. Darwin lifted the whole matter out of 
the field of mere transcendental speculation by the theory of natural 
selection, a perfectly intelligible mechanism by which the result might 
he brought about. Science will always prefer a material modus operand* 
to anything so vague as the action of a tendency. 
Lamarck’s second principle deserves much more serious consideration. 
To be perfectly fair, we must strip it of the crude illustrations with 
which he hampered it. To suggest that a bird became web-footed by 
persistently stretching the skin between its toes, or that the neck of a 
giraffe was elongated in the perpetual attempt to reach the foliage of 
trees, seems almost repugnant to common sense. But the idea that 
changes in climate and food— i.e., in the conditions of nutiition 
generally—may have some slow but direct influence on the organism, 
seems, on a superficial view, so plausible that the mind is very prone to 
accept it. Mr. Darwin has himself frankly admitted that he thought 
he had not attached sufficient weight to the direct action of the environ¬ 
ment. Yet it is extremely difficult to obtain satisfactory evidence of 
effects produced in this way. Hoffmann experimented with much pains 
on plants, and the results were negative. And Mr. Darwin confessed 
that Hoffmann’s paper had “ staggered ” him. 
Organic evolution still, therefore, seems to me to be explained in the 
simplest way as the result of variation controlled by natural selection. 
Now, both these factors are perfectly intelligible things. Variation is a 
mere matter of everyday observation, and the struggle for existence, 
which is the cause of which natural selection is the effect, is equally so. 
If we state in a parallel form the Lamarckian theory, it amounts to a 
tendency controlled by external forces. It appears to me that there is 
no satisfactory basis of fact for either factor. The practical superiority 
of the Darwinian over the Lamarckian theory is, as a working hypothesis, 
immeasurable. 
The new Lamarckian school, if I understand their views correctly, 
seek to re-introduce Lamarck’s “ tendency.” The fact has been admitted 
by M r. Darwin himself that variation is not illimitable. No one, in fact 
has ever contended that any type can be reached from any point. For 
example, as Weismann puts it, “ Under the most favourable circum¬ 
stances a bird can never become transformed into a mammal.” It is 
deduced from this that variation takes places in a fixed direction only, 
and this is assumed to be due to an innate law of development, or, as 
Weismann has termed it, a “ phyletic vital force.” But the introduction 
of any such directive agency is superfluous, because the limitation of 
variability is a necessary consequence of the physical constitution of 
the varying organism. 
It is supposed however, by many people that a necessary part of 
Mr. Darwin’s theory is the explanation of the phenomenon of variation 
itself. But really this is not more reasonable than to demand that it 
should explain gravitation or the source of solar energy. The investi¬ 
gation of any of these phenomena is a matter of first-rate importance. 
But the cause of variation is perfectly independent of the results that 
flow from it when subordinated to natural selection. 
VARIATION IN PLANTS. 
Though it is difficult to establish the fact that external causes- 
promote variation directly, it is worih considering whether they may not 
do so indirectly. Weismann, like Lamarck before him, has pointed out, 
as others have also done, the remarkable persistence of the plants and 
animals of Egypt; and the evidence of this is now even stronger. We 
at Kew owe to the kindness of Dr. Schweinf urth a collection of specimens 
of plants from Egyptian tombs, which are said to be as much as 4000 
years old. They are still perfectly identifiable, and, as one of my 
predecessors in this chair has pointed out, they differ in no respect from 
their living representatives in Egypt at this day. The explanation which 
Lamarck gave of this fact “ may well,” says Sir Charles Lyell, “ lay 
claim to our admiration.” He attributed it, in effect, to the persistence 
of the physical geography, temperature, and other natural conditions. 
The explanation seems to me adequate. The plants and animals, wc 
