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Insectivorous Plants

To Darwin, certainly, we owe much of our knowledge of those plants which may be called insectivorous plants, and to, him, therefore, we make acknowledgment. The pitcher plants and the Utricularias, as we have seen, derive their nutriment from organized matter, by absorbing the results of its decomposition. The plants now to be considered are higher in the scale of being, they possess organs for a true digestion and assimilation, and exhibit, in addition to these peculiarities, other phenomena which have been supposed to be confined to the animal world.

The first of these plants which may be called truly insectivorous is a tiny aquatic plant found in Europe, Asia, and Australia. A search of many days through a number of botanical periodicals has brought to light no single fact in addition to what Darwin has recorded. The botanists all seem to be on excellent terms with the Aldrovanda; they allude to it in their classifications, and use it as illustration with an easy and off hand familiarity which is very tantalizing to one who is seeking information; but, with the exception of Cohn and Darwin, they tell us absolutely nothing about its life-history.

According to Darwin, then, and to Cohn, the Aldrovanda is a water-plant, destitute of roots and floating freely in its native element; the petioles, or leaf stalks, grow out radially from the stem; these are broad, and terminate in from four to six slightly divergent spines, each tipped with a stiff bristle. The leaf grows in the midst of these projections; it is bilobed, and the two lobes stand apart about as far as the two valves of a living mussel-shell. The hinge of the two valves is the midrib, and this projects somewhat beyond the leaf itself, and is also armed with a bristle.

When the two valves are opened and pressed flat, the impression to the eye is of two circles so cutting each other that the circumference of each passes through the center of the other. The midrib forms the common chord which subtends the four arcs.

The overlapping portion of the circles is seen to be darker than the other, and between these two parts of each lobe there is a wide difference of structure and function. The darker segment of each lobe possesses the digestive and muscular apparatus of the higher species of insectivorous plants, while the lighter crescent-shaped portion is covered with absorbent quadrifid processes with which we have already become familiar in the Utricularias.

It is certainly very wonderful that we should find in an obscure and insignificant plant like the Aldrovanda, on one tiny leaf, a perfect representative of each of the two kinds of carnivorous plants, with the peculiar and delicate apparatus of each for the appropriation of organic matter.

The Aldrovanda supplies the link between the two distinct modes of nutrition in this class of plants, as the class supplies the link between the two great kingdoms of organic nature. The absorption of decomposed matter, performed by the quadrifid processes on the outer portion of the leaf, has already been described in the case of the Utricularia. The digestive process of the glands upon the inner portion will appear as we study the Drosera and

Dionxa, to which it bears a close resemblance, especially to the latter. Indeed, Darwin speaks of the Aldrovanda as a miniature aquatic Dionaea.