SPIRAL TORSION IN PLANT-GROWTH 191 
protected from such interruption. Ringing or tight ligatures 
round the base of a stem, i.e., below its lowest branches or 
leaves, will, therefore, stop growth below them, though they 
will not kill a tree. We have known a wire loop gradually saw 
right through a stem which healed up as it passed, so that the 
tree continued standing and alive. On the other hand, the 
elaborated sap checked in its passage down the bast produces 
the swelling usually seen above a ringing or ligature. 
The mechanism by which the unelaborated sap rises to 
the summit of lofty trees still presents problems not solved to 
the satisfaction of physiologists. Transpiration from the leaf- 
surfaces, no doubt, does much ; the rarefaction of the air-bubbles 
in the wood vessels by the removal of their oxygen may also 
contribute a “ negative pressure ” ; and we have to remember 
that transpiration is a vital process, that the wood vessels are 
filled with a column of water interrupted by air-bubbles, a 
“ chapelet de Jamin,” as it is termed, and that, though consist- 
ing of capillary tubes, they have thickened walls and thinner 
regions of permeable membrane or “pits.” Though, therefore, 
as Strasburger has shown, the sap can traverse a zone of dead 
wood, this does not prove its ascent, initiated below by root- 
pressure and drawn upwards by transpiration, to be a non- 
vital process. The difficulties may not be all solved ; but there 
is no reason to complicate matters by loose phraseology. 
SPIRAL TORSION IN PLANT-GROWTH. 
VERY interesting essay on “ Spirals in Nature and 
in Art ” has been recently published by Mr. Theodore 
Cook. The author’s main purpose is to show that 
a certain beautiful spiral staircase is the work of 
Leonardo da Vinci, and was suggested to the Master by the 
shell of a species of Valuta, Leonardo’s careful study of shells 
being well known to all students of his writings. Unfortu- 
nately, Mr. Cook has to admit that he is not himself a 
naturalist, while his subject is one which for anything like 
a complete exposition requires a considerable knowledge of 
molluscan development, and of the mathematics of curves. 
He has in consequence only touched the fringe of his subject 
on its natural history side. Our attention has been redirected 
to the question by some photographs, by Mrs. J. J. H. 
Teall, of a Cedar growing in the garden of Walter Harvey, 
Esq., at Dulwich, which have been sent us by M. J. Teesdale, 
Esq., and of which we here give a reproduction. 
There are cases of normal spiral form in the Vegetable 
Kingdom, such as the alga Ruellia, or the inflorescence of the 
Ladies-tresses Orchid (Spiranthes) ; but perhaps cases of spiral 
