PLANT COMPANIONSHIP (SYMBIOSIS) IN
THE FOREST.
By Prof. G. S. BOULGER, F.L.S.. F.G.S. (Vice-President).
[Being Abstract of an Address delivered at the Masting in Epping Forest, on
July 10th, 1897.]
AMONG the plants we have seen to-day are several illustrative of certain
recent conclusions as to mutual dependence (Symbiosis) among plants. It
has long been recognised that, in addition to those familiar normal independent
plants—plants with well-developed roots in the soil and green leaves exposed
to light and air, for which some years ago I proposed 1 the name "auto-
phytes,"—there are various other types of nutrition, for which I proposed
the collective term "heterophytes," plants of more or less abnormal nutri-
tion. There are the familiar parasites, with reduced leaves and little or no
chlorophyll, such as the Broom-rapes (Orobanche), the saprophytes, similar in
aspect but living mainly upon decaying organic matter, such as leaf-mould,
of which the Bird's-nest Orchis (Neottia nidus-avis) is a characteristic
example, and the insectivorous plants, such as the Sundews (Drosera),
with reduced root systems, and dependent largely upon nitrogenous food of
animal origin.
But, besides these familiar types, there are others, some of which are
of an interestingly intermediate character. The nutritional abnormalities of
which I wish mainly to speak at present have reference to two chemical
elements—the two most characteristic of organic beings—carbon with its
capacity for forming complex and polymorphic compounds, and nitrogen with
that distinctive inertness which renders so many of its compounds unstable
even to the degree of explosiveness. Most educated people, even those with
no special knowledge of physiology, are familiar in a general way with the
usual method in which the autophyte obtains its carbon, how the protoplasm
in the presence of chlorophyll and under the influence of sun-light decom-
poses the carbon dioxide of the atmosphere ; but the connection between a
partial cessation of this chlorophyllian function and a partial degradation of
the chlorophyll has not been so widely noticed. Young oak-leaves in spring
are, as you know, as red as many leaves and ripening fruits in autumn ; a
similar reddening, perhaps from the presence of that chlorophyllan, possibly an
oxide, which forms on exposure in an alcoholic solution of chlor-
ophyll, is common in the leaves of Sundews and in those of
various Pitcher-plants ; and it exists, under a more purple form, in
well-known varieties of the Beech and the Hazel, and very frequently in the
leaves of the Cow-wheat (Melampyrum). Now this last-mentioned plant—
common on the Forest—belongs to a sub-order of the Scrophularinae, to
which belong also the Yellow and Red Rattles, the Bartsia and the Eye-
brights, which are well-known to be partially parasitic upon the roots of
grasses ; and it is also partially saprophytic, flourishing among decaying leaves
and clinging with copious rootlets to any chance fragment of manure. The
1 "Plant Nutrition," Gardener's Chronicle, vol. ix. (1878.)