582 
This experiment I have repeated since reading Wiesner’s 
book, and have found the results to be the same. The 
conclusion is inevitable and is in this case absolutely 
destructive of Wiesner’s theory of ‘ Zugwachsthum.” 
This theory he grounds on the following experiment (p. 
69), in which he makes use of Sachs’s method of observing 
heliotropism :—Seedlings growing in small vessels are 
fixed in the place of the minute-hand of a large clock, so 
that each seedling is at right angles to the axis of rotation, 
and rotates like the hand of the clock ; they are then illu- 
minated by light which is parallel to the axis of rotation, 
and therefore each seedling has one side constantly illumi- 
nated by light striking it at right angles. Owing to the 
constant rotation the effect of weight is eliminated, and 
thus any curvature which occurs cannot be due to 
“Zugwachsthum.’”’ Wiesner states that whereas the seed- 
lings on the klinostat (Sachs’ name for this instrument); 
were only curved in their upper parts; plants growing 
normally without being subjected to rotation were curved 
down to the ground. This seems at first a conclusive 
argument against our view, but I shall show that in the 
case of two plants, cabbage and Phalaris, it is not so. 
We expressly stated (p. 479) that our experiments on 
cabbages were made on young seedlings “about half an 
inch or rather less in height,” because when the plants 
have grown to an inch and upwards in height the lower 
part ceases to bend heliotropically. Now Wiesner’s 
experiments were made confessedly on seedlings whose 
lower part was growing slowly, and which were therefore 
probably older than those which we employed for our 
experiments. When Wiesner made his rotating experi- 
ment with yousg cabbage seedlings they became curved 
down to the ground. This proves that the curvature 
which occurs near the ground in young cabbage seedlings 
is not due to weight ; and this is the very curvature which 
we have shown not to occur unless the upper part is illu- 
minated. Ido not attempt to explain Wiesner’s experi- 
ments on old cabbage seedlings, but those made with 
young ones are alone of importance for us, and they are 
conclusively on our side. 
With regard to Phalaris J] regret that I cannot confirm 
Wiesner’s results, who states that these seedlings behaved 
like the dicotyledons experimented on; ze. that when 
grown on the rotating apparatus they do not become bent 
down to the ground. I have experimented with young seed- 
lings such as we should have used for the experiments on 
transmission of the light-stimulus, and found that many 
of them became well bent down to the ground. But it 
should be remarked that in some cases a certain amount 
of difference in this respect was observable between the 
plants on the klinostat and normal ones. 
FRANCIS DARWIN 
(To be continued.) 
OUR BOOK SHELF 
Through Siberia. By Henry Lansdell. 
with illustrations and maps. 
and Co., 1882.) 
IT is obvious that much scientific information cannot be 
expected from a traveller who was, to use his own ex- 
pression, “flying across Europe and Asia,” and who 
crossed Siberia from Ekaterinburg, in the Ural Moun- 
tains, to Tobolsk in the North, Barnaoul in the Altai, 
Two volumes, 
(London: Sampson Low 
NATURE 
Arias oa. Nate Ft ae tp 
“i Somes aN ee 
[April 20, 1882 
and Nikolaevsk on the Pacific, a distance of 6600 miles, 
in seventy-eight days, and whose aim was, during this 
very short time, to investigate the situation of Russian 
prisons. The author has, however, supplemented his 
own somewhat superficial observations by information 
obtained from good sources. The book is provided with 
many illustrations, partly taken from other works (without 
quoting the source from which they are taken), and partly 
from new photographs. These are sometimes very good, 
but sometimes they convey quite false ideas, as, for 
instance, the photograph of a “ Buriat girl,” who obviously 
is a metis, having very little in common with true Buriats, 
POR 
LETTERS TO THE EDITOR 
[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. 
No notice is taken of anonymous communications. 
[The Editor urgently requests correspondents to keep their letters 
as short as possible. The pressure on his space is so great 
that it ts impossible otherwise to ensure the appearance even 
of communications containing interesting and novel facts.) 
Limulus 
IN a criticism published in the American Naturalist for 
April, 1882, on Prof. Ray Lankester’s recent most able memoir, 
entitled ‘‘Limulus an Arachnid,” Mr, A. S. Packard, whose 
most important researches on Limulus are familiar to all 
zoologists, and to whose courtesy I am indebted for a copy of his 
criticism, after stating other grounds which lead him to differ in 
opinion from Prof Lankester as to the close relationship of the 
King Crab and the Scorpion, quotes in his final paragraphs 
extracts from published letters written by my late lamented friend 
and shipmate, R. von Willemoes-Suhm, from on board H.M.S. 
Challenger, at the Phillipine Islands and Japan in February and 
May, 1875, concerning certain Arthropod embryos which he had 
had under observation at Zamboangan, and which he then sup- 
posed to be the larvee of Limulus rotundicauda. As Von Suhm 
and I worked together for more than two years daily with our 
microscopes within two feet of one another, we naturally dis- . 
cussed all that we did end observed in common, and we frequently 
talked about these supposed Limulus embryos, and looked at them 
together. It is as well, therefore, since the statements concerning 
them are being made use of to assist in disproving the position 
assumed by Prof. E. van Beneden, Prof, Lankester, and others 
as to the Arachnid nature of Limulus, a position of the strength 
of which I am myself persuaded, that I should state in print, 
that long before his death Von Willemoes-Suhm was completely 
convinced that he had been misled as to the larve, and told me 
that he felt sure they were not those of Limulus at all, but 
belonged to a Cirrhiped of some sort. I some time ago told my 
friend, Prof. E. van Beneden, who inquired on the matter, that 
such was Von Suhm’s final conclusion. And I also long ago 
told Prof. Lankester, and this is no doubt the reason why no 
reference to Von Suhm’s letters was made by the latter in his 
memoir. 
It must be remembered that the only evidence in favour of 
Von Suhm’s Nauplius larvz being those of Limulus, lay in their 
general appearance, which simulated to some extent that of an 
adult Limulus, and in the fact that they were caught with the 
tow-net in Zamboangan harbour, a locality at which Lzmeeleus 
rotundicauda occurs. H. N. MosELEy 
Oxford, April 15 
Silurian Fossils in the North-West Highlands 
THE publication of Dr. Heddle’s geological and mineralogical 
map of Sutherland, which was noticed in NArurg, vol. xxv. 
p- 526, calls to mind some curious points with reference to that 
region—points on which we should like to have some further 
and more definite information, 
Dr. Heddle quite acquiesces in the general accuracy of the 
stratigraphical conclusions arrived at by Murchison and his 
colleagues, and, as may be gathered both from his map and 
writings, has seen no cause whatever to induce him to believe 
either in the great fault of Prof. Nicol, or in the unconformity 
alleged by Dr. Hicks to exist in the adjacent county. 
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