Natural- Historical Collections. 301 
stralian animals, insomuch that they can now scarcely be regarded as rarities 
even in this country. They are precisely similar insform and somewhat inferior 
in size to the wild and tame swans of the old world ; but are perfectly black in 
every part of their plumage, with the exception of the primary and a few of the 
secondary quill-feathers, which are white. Their bill is of a bright red above, 
and is surmounted at the base in the male by a slight protuberance, which is 
wanting in the female. Towards its anterior part it is crossed by a whitish 
band. The under part of the bill is of a grayish white; and the legs and feet 
are of a dull-ash colour. In every other respect, except in the mode of convolu- 
tion of its trachea, this bird so perfectly corresponds with its well known con- 
geners, that it is only necessary to refer to the articles in which we shall hereafter 
describe those beautiful species for an account of the characters which are com- 
mon to them all. 
The black swans are found as well in Van Diemen’s Land as in New South 
Wales and on the western coast of New Holland. They are generally seen in 
flocks of eight or nine together, floating on a lake; and when disturbed, flying 
off like wild geese in a direct line one after the other. They are said to ‘be eXx- 
tremely shy, so as to render it difficult to approach within gunshot of them.— 
Gardens and Menagerie of the Zoological Society, No. III. 
Influence of Soil on Roots.— If a cucumber,” says Sir James Smith in his 
Lectures, of which MS. notes are now before me, “ is planted; and after the 
branches shoot there is placed a stone in the way of either of them, the branch 
will turn off and avoid it without towching the stone, but describing a circle 
around it. When it has passed the stone, however, it will go on in a straight 
line.”” Sir James explains this by the well-known law of plants always approach- 
ing the light, the cucumber turning round to get out of the shadow of the stone. 
Roots follow a very different law, always endeavouring to get away from the 
light ; and, accordingly, so far from avoiding a stone or other obstacle, they often 
cling closely around it, and sometimes even mould their forms upon the hard 
substances with which they meet. This is well exemplified in the root of an alder 
‘tree (Alnus glutinosa, Betula Alnus, Linn.), which my little boy found in his 
searches after fresh-water shells for his collection. The root was embedded 
among the gravel formed by the Ravensbourne river which passes the bottom of 
my garden ; and it has exactly moulded itself on every stone which it met with 
in its course. In the same manner roots are much influenced in their forms by 
the soils in which they grow. Of this I lately gave the following illustration 
in the Atheneum, from the familiar instance of fibrous and bulbous roots :— 
When plants with fibrous roots are placed in certain situations, they are apt to 
change their fibrous structure for a bulbous one, in the same way as the water 
crowfoot (Ranunculus aquatilis) has scolloped leaves above, and minutely winged 
leaves below water. ‘The change from fibrous to bulbous roots, and the contrary, 
is markedly exemplified in some of the grasses, particularly in Timothy grass. 
(Phleum) and fox-tail grass (Alopecurus). Before this change of form was 
discovered, botanists frequently described the same grass under dia rent names ; 
a circumstance which occurred with regard to Alopecurus geniculatus, and 
Phleum pratense. Leers seems to have been the first to discover that transplant. 
ing into a light rich soil tends to change the bulbous into the fibrous structure.— 
J. RENNIE, Loudon’s Mag. No. X. 
Habits of the Cayman or Alligator of Guiana.—Dr. Hancock, who has iden- 
tified himself with the natural history of Guiana, has communicated to Professor 
Jameson the following interesting observations on the habits of the cayman or 
alligator, which abounds in most of the great rivers of Guiana, excepting the 
Cassiquiari and Rio Negro.* 
* Dr. H. supposes their absence i in these rivers to be owing to the prevalence 
of the porpess, * the natural enemy’ ” of the cayman. 
