Fig. 301.—Arum maculatum. The spathe (h) in B is longitudinally divided.
B. Calleæ. Flowers hypogynous, naked, ☿.—Calla (C. palustris). All flowers in the spike are fertile, or the upper ones are ♂; 6–9 stamens; ovary unilocular with many basal ovules. Marsh-plants with creeping rhizome and cordate leaves.—Monstera, Rhaphidophora, etc.
Fig. 302.—Colocasia Boryi.
C. Arineæ. Flowers monœcious, naked, ♂-flowers on the upper, ♀ on the lower part of the spadix.—Arum (Fig. [301]). The spadix terminates in a naked, club-like portion (k); below this is a number of sessile bodies (rudimentary flowers), with broad bases and prolonged, pointed tips (b); underneath these are the ♂-flowers (m), each consisting only of 3–4 short stamens, which eject vermiform pollen-masses through the terminal pores; then follow, last of all, ♀-flowers (f), each of which consists of one unilocular ovary, with several ovules. Perennial herbs, tuberous, with cordate leaves.—Dracunculus; Biarum; Arisarum; Pinellia (Atherurus) ternata with leaves bearing 1–2 buds. Zantedeschia æthiopica (Richardia, Nile-lily); ♂, 2–3 stamens; ♀ with 3 staminodes, 1–5-locular ovary (S. Africa.)—In some genera sterile flowers are present between the ♂ and ♀ portions of the spadix (e.g. in Philodendron); in Ambrosinia a lateral, wing-like broadening of the axis of the spadix divides the cavity of the spathe into two chambers, the anterior containing one ♀, and the posterior 8–10 ♂-flowers in two series; in some the stamens in the single ♂-flowers unite and form a columnar “synandrium” (e.g. in Dieffenbachia, Colocasia, Alocasia, Caladium, Taccarum, Syngonium). A remarkable spadix is found in Spathicarpa; it is united for its entire length, on one side, with the spathe, and the flowers are arranged upon it in rows, the ♀ to the outside, and the ♂ in the middle (Zostera has a similar one).—Pistia similarly deviates considerably, it is a floating water-plant, with hairy, round rosettes of leaves; in it also the spathe and spadix are united; at the base a ♀-flower is borne, which consists of one unilocular ovary, and above several ♂-flowers, each composed of two united stamens.
Biology. The inflorescences are adapted for insect-pollination; they are protogynous, since the viscous, almost sessile stigmas come to maturity and wither before the pollen, which is generally dehisced by apical pores, is shed; some pollinate themselves freely by the pollen from the higher ♂-flowers falling upon the ♀-flowers below them, and in some it is conjectured that the pollination is effected by snails. The coloured spathe, and the naked end of the spadix (often coloured) of certain genera function as the coloured perianth in other orders; during flowering a very powerful smell is often emitted. Arum maculatum is worthy of notice; small flies and midges creep down into the spathe, between the sterile flowers (Fig. [301] b), which are situated where the spathe is constricted, and pointing obliquely downwards prevent the escape of the insects; in the meantime, the stigmas are in a condition to receive any pollen they may have brought with them; after pollination the stigmas wither, and exude small drops of honey as a compensation to the flies for their imprisonment; after this the anthers (m) open and shed their pollen, the sterile flowers wither, and the insects are then able to escape, and enter and pollinate other inflorescences.—In many, a rise of temperature and evolution of carbonic acid takes place during flowering; a spadix may be raised as much as 30°C. above the temperature of the surrounding air.—Again, under certain conditions, many species absorb such large quantities of water by their roots that water is forced out in drops from the tip of the leaf; this may often be observed in Zantedeschia.
About 900 species in 100 genera. Home, the Tropics, especially S. America, India, and the Indian Islands, preferably in shady, damp forests growing as epiphytes upon trees, and on the banks of streams. Outside the Tropics few are found. Acorus calamus was introduced into Europe from Asia about 300 years ago; it, however, never sets any fruit, as the pollen is unfertile. In England Arum maculatum is a very common plant; this and A. italicum are the only native species. Colocasia antiquorum comes from Polynesia and the Indian Islands, and also Alocasia macrorrhiza. Fossils in Cretaceous and Tertiary.
Uses. Many species have pungent, and even poisonous properties (e.g. Dieffenbachia, Lagenandra, Arum), which are easily removed by boiling or roasting; the rhizomes of many species of Caladium, Colocasia (C. antiquorum, esculenta, etc.), are very rich in starch, and in the Tropics form an important source of food. An uncommon occurrence in the order is the highly aromatic rhizome of Acorus calamus; this contains calamus-oil and acorin which are used in perfumery. Many are ornamental plants, e.g. Zantedeschia æthiopica (South Africa), generally known as “Calla,” and Monstera deliciosa; many other species are grown in greenhouses.
Order 6. Lemnaceæ (Duck-weeds). These are the most reduced form of the Spadicifloræ. They are very small, free-swimming water-plants. The vegetative system resembles a small, leaf-like body (Fig. [303] f-f), from which roots hang downwards; this branches by producing a new, similar leaf-like body, which springs from a pocket-like hollow (indicated by a dotted line in the figure) on each side of the older one, at its base (or only on one side). The branching is thus dichasial or helicoid (Fig. [303] A, where f, f′, f″, f″′ indicate shoots of 1st, 2nd, 3rd, 4th generations respectively). The leaf-like bodies are, according to Hegelmaier, leaf-like stems, and thus Lemna has no other leaves than the spathe and the sporophylls; according to the investigations of Engler they are stems whose upper portion (above the “pocket”) is a leaf, which is not sharply separated from the underlying stem-portion. The inflorescence is a very much reduced Araceous-spadix, consisting in Lemna of 1 or 2 stamens of unequal length (1-stamened ♂-flowers), 1 unilocular carpel (♀-flower), and 1 thin spathe (B). [The same is found in Spirodela polyrrhiza, etc., whose daughter-shoots begin in addition with 1 basal-leaf. Wolffia arrhiza, etc., have no roots, no spathe, and only 1 ♂-flower in the inflorescence (Engler).]—On the germination of the seed a portion of the testa is thrown off as a lid, so that an exit is opened for the radicle.—19 species. In stagnant fresh water, both Temp. and Tropical.—In Europe the species are Lemna minor, trisulca, gibba; Spirodela polyrrhiza, and Wolffia arrhiza, the smallest Flowering-plant.
