366 
NATURE 
[ Feb. 15, 1883 
In the comments which I added to the views of these eminent 
observers, wherein I mentioned those circumstances that seemed 
to me to tend in the direction of their support, I was, of course, 
unable to include, as I would if possible have done, a statement 
of the opinions of such noted authorities as Dr. Steube and 
Herr von Siebold, the results of whose investigations have so 
recently been given to the press, and which are cited in the 
article that elicits this letter. J. J. REIN 
Marburg, Germany, February 8 
Hovering of Birds 
I REGRET that I did not notice until to-day that Mr. Airy, in 
his letter published in NA1URE, vol. xxvii. p, 294, specially re- 
ferred to ‘‘hovering with perfectly motionless wings” as being 
that for which an upward slant of wind is, as he believes, 
absolutely requisite to enable the bird to do so. 
Is the term ‘‘hovering’’ applicable to the examrles given by 
Mr. Airy of gulls and hawks floating as it were with motionless 
wing along hillsides and cliffs ? 
I have always associated ‘‘ hovering” with the flapping or 
fluttering of the wings, as is invariably noticed when terns or 
hawks are looking for their prey either over land or water. 
February 10 eas 
Intelligence in Animals 
IN his letter in NATURE, vol. xxvii. p. 337, Mr. J. Birming- 
ham does not mention what kind of bear it is that throws down 
pieces of rock ‘‘in order to ca*ch the bareins,” as told by the 
Kamtschadales ; but the Eskimos have a somewhat similar story 
of the white bear, when attacking the walrus, the largest of 
which, with their formidable tusks, Bruin generally avoids. 
The circumstance was told me by an eye-witness, a very 
truthful and honest Eskimo of Repulse Bay. He said: ‘‘I and 
two or three other Innuit were attempting to approach some walrus 
in winter, lying on the ice close to the water, kept open by the 
strong current, in Fox’s Channel. As we were getting near 
we saw that a large white bear was before us. He had reached 
in the most stealthy manner a high ridge of ice, immediately 
above where the walrus were lying ; he then seized a mass of 
ice? in his paws, reared himself on his hind legs, and threw the 
ice with great force on the head of a half-grown walrus, and 
then sprang down upon it.” 
The Eskimos then ran up, speared the bear, and found the 
walrus all but dead, thus securing both animals. I should add 
that the bear threw the ice as if he was “‘left-pawed.” 
Kensington, February 10 J. Rar 
WHILE spending the late winter months at Paignton, in 
Devon, I frequently watched, through a telescope, shore birds 
of various kinds stalking game on the low-tide sands. These 
abound with sand-eels, which lie, perfectly concealed, about an 
inch below the surface, and are caught in the following way Ly 
the gulls. 
Standing close to the water’s edge, the birds tread the wet 
sand into soft puddles by rapid alternate movements of their feet, 
and when a sand-eel, thus disturbed, makes a dart for the sea, 
he is instantly taken by a skilful but leisurely-looking snap of 
the beak. 
Sand-eels bury themselves without leaving any marks on wet 
sand, and the gulls were always seen steadily and tentatively 
beating over the ground in the way I bave described. They 
took, each, a fish a minute, perhaps, and impressed me with 
the idea that some thoughtful ancestral gull had deserved well 
of his race for the invention of such an easy logical way of 
picking up a living. D, PIDGEON 
Holmwood, Putney Hill, February 7 
The Sea-Serpent 
On reading the letter of W. Steadman Aldis in NATURE 
(vol. xxvii. p. 338) yesterday, I was reminded by a person 
present that some years ago, when in Orkney, I pointed out 
an appearance that most people unaccustomed to witness it 
might have taken for a great sea-monster. This was no hing 
more or less than some hundreds of cormorants or ‘scarps ” 
* It may be questioned how the bear could find a lump of detached ice. 
The strong current mentioned is constantly breaking up the ice into small 
pieces, 
flying in a continuous line close to the .water, the deception 
being increased by the resemblance of a head caused by several 
“* scarps” in a cluster Aeading the column, and by the ‘‘ /ampy” 
seas of a swift tideway frequently intervening and hiding for an 
instant part of the black lines, causing the observer to—not un- 
naturally—imagine that the portions so hidden had gone under 
water. The speed of the cormorant on the wing may be fairly 
estimated at thirty miles an hour or more. J. RAE 
Kensington, February 10 
The “ Zoological Record” 
I sHOULD like to point out a slight error in the last impression 
of NATURE (p. 311). In your notice of the Zoological Record, 
1881, it is stated that no separate paper seems to have appeared 
in 1881 exclusively devoted to the group Octactizie. I should 
mention that Prof. Nicholson’s book on ‘‘ Monticulipora,” 
his paper on the skeleton of ‘‘ Tubipora,” and Mr. Wilson’s 
paper on the development of ‘‘ Renilla,” all appeared in 1881, 
and were duly recorded by me. SyDNEY J. Hickson 
Anatomical Department, Museum, Oxford, February 5 
STEVE-TUBES 
vEN CAREFUL examination by E. Russow (Amz. Sez. 
Wat. xiv. 1882, Nos. 3 and 4) of the structure and 
development of sieve-tubes leads him to the following 
general conclusions. 
In all vascular plants examined, the sieve-tubes exhibit 
a remarkable agreement in structure, always expressed 
by the presence of callus. The sieve-punctation appears 
to be wanting in /soefes, and possibly also in the Marat- 
tiaceze. It is not, when present, confined to the sieve-tubes, 
but occurs also in the parenchyma of the secondary liber. 
It is often difficult to decide whether these punctations 
are actually perforated; but this is clearly the case 
wherever the sieve is traversed by callose cushions or 
striz, or by connecting filaments; the presence of callus 
is not of itself sufficient to indicate perforation, for its 
formation certainly precedes the perforation of the mem- 
brane. In conifers the punctations between the sieve- 
tubes and the cells of the medullary rays are provided 
with callose cushions only on the side of the sieve-tubes, 
and the punctations remain closed. 
The development, accumulation, and final disappear- 
ance of the callus indicate that it is not a product of 
transformation of the cellulose, but that it is separated 
from the contents of the sieve-tubes ; its accumulation 
round the perforations is proportionate to the freedom 
and duration of the intercommunication that takes place 
through them; this communication probably continues as 
long as the strie of the callus remain clearly developed, 
and ceases when these disappear, close up the sieve-pores, 
and end the function of the sieve-tubes. 
In gymnosperms and vascular cryptogams, mucilagi- 
nous filaments are never to be seen traversing the callose 
cushions, although there is always a certain ainount of 
communication between the elements of the sieve-tubes. 
The special function of the sieve-tubes is probably always 
maintained wherever striaz cross the callose cushions. 
The large number of plants in which the sieves are tra- 
versed, both in summer and winter, by mucilaginous 
filaments, and the large number in which no such fila- 
ments are at any time observable, contradicts the idea 
that the function of the callus is to close the sieve-pores 
during the dormant season. 
Much less callus is deposited in the sieve-tubes of 
closed fibrovascular bundles, especially in permanent 
organs, than in those of open bundles which increase in 
thickness from the activity of their cambium. This dif- 
ference corresponds to a difference in the nature of the 
contents, and in the duration of the activity of the sieve- 
tubes. While in gymnosperms and dicotyledons the 
active period of the sieve-tubes rarely exceeds two years, 
in monocotyledons and vascular cryptogams it lasts as 
long as the organ itself. A stem of Adsophila, at least 
