March 15, 1883 | 
NATURE 
465 
Ranunculus ficaria, the lesser celandine, which produces 
its foliage in early spring from buried tubers, and so anti- 
cipates other plants, having the air all to itself for a 
couple of months, after which it gets overshadowed by 
later comers. The same type recurs pretty closely in the 
radical leaves of its allies, R.auricomusand R. parviflorus, 
as also somewhat more remotely in the ivy-leaved crow- 
foot, 2. hederaceus, which creeps, unimpeded, over soft 
mud. Many early spring plants have lower or radical 
leaves at least of this reniform type, because they grow in 
comparatively unoccupied ground. As an example, take 
ground-ivy, Wefeta glechoma (Fig. 16). The violets re- 
present a closely similar case. Many of these plants, 
Fic. 15.—Typical leaf of Tusstlago Fic. 16.—WNefeta glecoma. 
genus. 
however, produce later on, when foliage grows thicker, 
much more lanceolate leaves. In the burdocks, docks, 
&c., this type is persistent. 
On the other hand, where the distribution of carbonic 
acid is most scanty, or where the competition is fiercest, 
or where the competing plants are supplied with no re- 
serve to enable them to send up shoots which overtop 
their competitors, immense subdivision into leaflets takes 
place, and these leaflets are often almost or quite filiform. 
The extent to which leaflets are subdivided depends upon 
the relative paucity of carbon in their environment; the 
general resulting form depends mainly upon the inherited 
type of venation. Among submerged aquatic plants, the 
Fic. 17.—Charophycium silvestre. 
filiform condition is habitual, because carbonic acid is so 
comparatively scarce in water. Among British species, 
the water violet, Hottonia palustris, is a good example. 
All terrestrial primroses have undivided foliage ; but in 
flottonia the leaves, still preserving the pinnate character 
of the venation, as in the common primrose, are cut into 
very deep segments, forming a close mass of narrow, 
linear, waving threads, more like a Chava than a flowering 
plant at a first glance. Uv¢ricularia shows the same result 
with a different ground-plan. In Myridophyllum, water 
milfoil, we have whorls of leaves each minutely subdivided 
| localities. 
into hair-like pinnate segments, and moving freely through 
their still ponds in search of stray carbon particles dif- 
fused in the water. A/zppuris has the separate Jeaves un- 
divided, but attains the same result by crowding its long, 
thin, linear blades in whorls of ten or twelve, so as closely 
to resemble an Lguisetum. Our common Ceratophyllum 
looks at first sight much like water-milfoil, but here the 
whorled leaves, instead of being pinnately divided, are 
repeatedly forked into subulate or capillary segments, the 
result of a branching rather than of a pinnate venation. 
Other instances will occur at once to every botanist. 
On land we get very much the same condition of things 
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Fic. 18.—Floating leaf of 7xafa natans. 
in the fierce competition that goes on for the carbon of 
the air between the small matted undergrowth of every 
thicket and hedgerow. The common weedy plants, and 
especially the annuals or non-bulbous perennials, which 
grow under such conditions, cannot afford material to 
push broad leaves above their neighbours’ heads, and 
they are therefore compelled to fight among themselves 
for every passing particle of carbon. Hence they are 
usually very minutely subdivided, though in a less waving 
and capillary manner than the submerged species ; their 
Fic. 19.—Submerged leaf of Trafa natans. 
leaflets are oftener flat, and definitely exposed on their 
upper surface to the sunlight. That essentially weedy 
family, the Umbellates, contains a great number of such 
highly segmented hedgerow leaves. Common wild cher- 
vil, Cherophyllum silvestre (Fig. 17), forms a familiar 
example: other cases are C. ¢emulum, Sison Amomum, 
many Carums, Genanthes, Pimpinellas, Daucus, Caucalis, 
&c., all of which belong by habit to greatly overgrown 
Compare these with the free-growing, almost 
orbicular, radical leaves of Astrantia and Sanicula, m 
