al 
March 8, 1883] 
NATURE 
439 
But in peripheral nervous mechanisms, such as those 
in the heart of the frog, where we have no such pro- 
vision, and the cells are not only few in number, 
Vit 
A.KARMANSK/ 
E.PRBMIBCNEN. SC 
Fic. 7.—View of the auricular septum in the frog (seen from the left side). 
n is the posterior, and 7’ the anterior cardiac nerve, ¢ is 4 horizontal 
portion of the latter nerve; 4 is the posterior, and 2’ the anterior auriculo- 
ventricular ganglion; #z is a projecting muscular fold. This figure is 
taken by the kind permission of my friend, M_ Ranvier, from his Legons 
d’Anatomie Générale, Année 1877-8.—Appareils nerveux terminaux, t. 6, 
p- 79. (Paris: J. B. Bailliére et Fils, Rue Hautefeuille 19.) 
but not arranged in strata, we find a special form of 
ganglion cell which seems constructed for this very 
purpose. This is the spiral cell described by Beale, 
AsKARMANS KI 
A.B.M . 
SS 
Fic, 8.—Part of the posterior cardiac nerve more highly magnified, showing 
the ganglia (Ranvier, of. cit. p. 106). 
in which we find one nerve-fibre twisted round and 
round in a way which reminds us of a resistance coil 
in a galvanic circuit. The object of this peculiar arrange- 
ment has, so far as I know, not been discovered ; but it 
seems to afford the exact mechanism which is wanted, 
in order to alter the distance two stimuli have to travel, 
and thus allow them to interfere with and inhibit each 
other. The occurrence of these ganglia in the heart and 
other viscera seems to afford in itself some support to the 
Fic. 9 —Spiral ganglion cell trom the paeumogastric of the frog. This figure 
is not taken from the cells in the cardiac nerves, as in them the connection 
between the spiral and straight fibres has not been clearly made out, but 
it is probable that these cells have a structure similar to the one figured 
(Ranvier, of. czt. pp. 114-20). a is the cell body, # the nucleus. 7 the 
nucleolus, ¢ nucleus of the capsule, /the straight fibre, g Henle’s sheath, 
sf spiral fibre, g’ its gaine, ~’ nucleus of Henle’s sheath (Ranvier, 
op. cit. p. 114). 
hypothesis here advanced; but we will defer the con- 
sideraticn of the mode in which inhibition occurs in the 
heart and other internal viscera, and pass on at present 
to the effect of various parts of the central cerebro-spinal 
system upon each other. 
T. LAUDER BRUNTON 
(To be continued.) 
LHE SHAPES OF LEAVES 
I.—General Principles 
ee leaf is the essential and really active part of the 
ordinary vegetal organism ; it is at once the mouth, 
the stomach, the heart, the lungs, and the whole vital 
mechanism of the entire plant. Indeed, from the strictest 
biological point of view every leaf must be regarded as to 
some extent an individual organism by itself, and the tree 
or the herb must be looked upon as an aggregate or 
colony of such separate units bound together much in the 
same way as a group of coral polypes or the separate 
parts of a sponge in the animal world. It is curious, 
therefore, that so little attention, comparatively speaking, 
should have been given to the shapes of the foliage in 
various plants. ‘‘ The causes which have led to the dif- 
ferent forms of leaves,’’ says Sir John Lubbock, “ have 
been, so far as I know, explained in very few cases.” 
Yet the origin of so many beautiful and varied natural 
shapes is surely worth a little consideration from the evo- 
lutionary botanist at the present day, the more so as the 
main principles which must guide him in his search after 
their causes are simple and patent to every inquirer. 
The great function of a leaf is the absorption of car- 
bonic acid from the air, and its deoxidation under the 
influence of sunlight. From the free carbon thus ob- 
tained, together with tne hydrogen liberated from the 
water in the sap, the plant manufactures the hydro-car- 
bons which form the mass of its various tissues. Vegetal 
life in the true or green plant consists merely in such 
deoxidation of carbonic acid and water, and rearrange- 
ment of their atoms in new form :, implying the reception 
of external energy; and this external energy is supplied 
by sunlight. We have thus two main conditions affecting 
