464 
NATORE 
[March 15, 1883 
THE SHAPES OF LEAVES? 
Il.—Extreme and Intermediate Types 
V HERE access to carbonic acid and sunlight is 
habitually unimpeded by the competition of other 
plants in any direction, the leaf of each species tends to 
assume a completely rounded form; the conditions are 
evenly distributed on every side of it. Such absolute 
freedom to assume the fullest foliar perfection is best 
found on the surface of the water. Hence most water- 
plants which have leaves lolling on the surface assume a 
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Vio Ness 
[ re: 
Fic. 10.—Lemna minor. 
more or less distinctly rounded shape, the venation and 
other details remaining in accordance with the ancestral 
habit. Foliage of this character is found in the water- 
lilies and many other aquatic plants. The little entire 
lenticular fronds of the common duckweed, Lemna minor 
(Fig. 10), which coats all our small ponds and ditches, 
form an excellent example of the tyre in question. Here 
the shape is almost orbicular; the edge is entire ; and 
the smallness of each separate frond is due to the minute- 
ness of the plant and the obvious necessities of its situation. 
In the waterlilies we get a similar example on a much 
larger scale, for these plants recline on broader and 
more permanent sheets of water, and draw nourishment 
from their large rhizome, sunk securely in the mud _ be- 
neath, and annually accumulating a rich store of food- 
stuffs for the growing foliage. Dep 
Mr. Herbert Spencer (by whose kind permission two 
accompanying diagrams are copied from “‘ The Principles 
of Biology’’) points out a distinction between the shapes 
adopted by such plants, according to their relations to a 
central axis. Inthe sacred lotus, Ne/wmbium spectosum 
¥ Continued from p. 442. 
(Fig. 11), the leaves grow up on long and independent 
footstalks, without definite subordination to any such 
axis; and they therefore assume an almost perfectly 
symmetrical peltate form. Inthe Victoria regia (Fig. 12) 
the footstalks, though radiating almost horizontally from 
a centre, are long enough to keep the leaves quite remote 
from one another; and here they assume an almost 
symmetrically peltate shape, but with a bilateralness 
indicated by a long seam over the line of the footstalk. 
The leaves of our own white waterlily, Mymphea alba 
(Fig. 13), are more closely clustered, and have less room 
to expand transversely than longitudinally; hence they 
are somewhat longer than broad, and have a cleft where 
the Victoria regia has only a seam. Limnanthemum 
shows the same type on a smaller scale. 
Among land plants, the conditions under which leaves 
2 ie 
Fic. 12.—Victoria regia. Fic. 13.—Nymphea alba. 
can fill out to the full rounded shape occur less frequently 
than among floating aquatic species ; still, even here a 
very interesting set of gradations may be observed. The 
best example of all is that given by the common American 
May-apple, Podophyllum peltatum, where the separate 
radical leaves grow straight up from a stout rootstock on 
very thick and tall stalks, so as to overshadow all the 
other vegetation ; and they assume a regular, circular, 
peltate form, exactly like a Japanese parasol. The radical 
leaves of our own English Cotyledon umbilicus (Fig. 14), 
| springing from a perennial rootstock, for the most part 
on bare walls or unoccupied hedgerows, are able simi- 
larly to expand without interference, and catch carbonic 
acid and sunlight to their hearts’ content. Hence they 
are orbicular and peltate, though they retain the charac- 
teristic crenate edge of most flat-leaved Crassulacee. 
| Fic. 14 —Cotyledon umbilicus. 
| But the upper leaves, springing from the flower-stalk, are 
| more bilateral, as shown in the figure, though even these 
| round out to a more or less orbicular form, owing to their 
| exceptional access to air and light. The so-called garden 
nasturtium, Zyopeolum majus, with leaves growing out 
at right angles into open space, has also peltate leaves, as 
has likewise the usually aquatic Hydrocotyle. L 
When the plant sends up leaves from a rich buried 
rootstock, so tall as to overshadow the surrounding vege- 
tation, but subordinated to a common centre, they usually 
assume the reniform shape. This type is particularly well 
seen in the various coltsfoots—for example, in Tussilago 
| farfare, 7. petasites, and T. fragrans (Fig. 15). Similar 
types occur in Asarabacca, and in the marsh marigold, 
Caltha palustris. Extremely similar to the leaf of Caérha, 
though on a smaller scale, is that of one true buttercup, 
