Fig. 77.—Seed of Zanonia macrocarpa.
Seeds are also in some instances invested with a dense down, as in the familiar example of the cotton plant, in which the seed is covered with the substance called "cotton." In some other plants, which are closely allied, this cotton is silky and shining (as in Bombax and Eriodendron), but this same silky substance invests the seeds in some of the Asclepiadaceae, which family is far removed from the above, and also from the Convolvulaceae, in which latter family there are instances of Ipomoea, the seeds of which are invested in one species with a substance like "silk-cotton," and in another with a substance resembling a native Indian cotton, approaching to the texture of wool.
<!-- image -->Fig. 78.—(a) Crested seed of Sarcostemma, (b) Echites scabra, (c) Willow-herb (Epilobium), (d) Milk Thistle (Silybum marianum).
It would not be difficult to go on repeating instances of such coincidences in fruits and seeds for many pages, but we must rest content with another series. Most persons are aware that the prevalent type of seed in the fir tree, or coniferous family, consists in a brown hard seed, with an extension of membrane into a kind of wing. Of course, there are different forms of pine seeds, some of which have no wing; but we desire to indicate that the winged type is repeated in other families, not at all related to the Coniferae. This is the case with the seeds of some of the species of Lagerstroemia, which are allied to our "purple loosestrife;" also in Cedrela, and some other genera in the natural order to which the mahogany tree belongs; and, to some extent, in Ailanthus, wherein there is an approach to the samara of the ash, the winged fruits being, in fact, "samarae," and not seeds. Fir cones themselves are almost imitated in the fruits of some of the palms, in so far as appearance goes, although in structure very different, and the scales are imbricated in the opposite direction; nevertheless they might pass for an imitation.
If we go still deeper into the structure of plants and investigate their secretions, we shall encounter here and there coincidences of strange significance. In the lettuce is repeated the narcotic milky juice of the poppy. In the American Loasaceae the stinging properties of the nettles. In the figs (Ficus) of India, the rubber trees of Para (Siphonia) and the Urceolas of Asia, we have in three different families, and to a certain extent in some others, plants furnishing the same kind of milky juice which consolidates into caoutchouc, or india-rubber. The acrid juice which is secreted by some of the Anacardiaceae has its analogue in the Euphorbiaceae. The smoke of the wood of Excoecaria agallocha when burnt is said to affect the eyes with intolerable pain; and so also the manchineel, which belongs to the same family, and that of another tree, referred to the Anacardiaceae. The native in Brazil poisons his arrows with the juice of the mandioca plant, which belongs to the Euphorbiaceae; the Fiji Islanders with that of an Antiaris, which is of the bread fruit family; and on the Orinoco the famous curare is obtained from a Strychnos. The ancient Briton obtained his blue dye from the woad (Isatis tinctoria), the Hindoo, and other Asiatics, from the indigo plant, and the Assamese from a Ruellia. We do not pretend to assert that these are all instances of mimetic resemblance, or that these, and scores of similar coincidences, would give any support to a theory of natural selection and survival of the fittest. All that we are justified in proposing is, that these circumstances should be borne in remembrance in connection with the strange coincidences of form to which we have devoted the preceding pages.
Amongst fungi there are also striking resemblances, which have been detailed more fully in another place. Special attention was first directed to this subject by Mr. Worthington Smith, who gave several rather striking examples, although the pairs are more closely allied than those selected amongst the flowering plants. Thus, one poisonous species, Agaricus (hebeloma) fastibilis, greatly resembling the edible mushroom, Agaricus (psalliota) campestris, came up in great numbers upon a mushroom bed, and might have caused a disastrous result, had not the fact been detected by an adept. Another instance was also that of a mass of fungi which made their appearance on a mushroom bed. At first sight these closely resembled the variety of an edible species which not unusually comes up in clusters on old beds; it has white spores, with a lobed and undulated white pileus, Agaricus (clitocybe) dealbatus. The imitating fungus had the same wavy cap, white colour, and fungoid odour, but the spores were pink, and its structural features were distinctly those of quite a different species, Agaricus (clitopilus) orcella. In this instance both were quite innocuous. Two wholly distinct, but very similar fungi commonly grow together on wood ashes, or scorched places, where charcoal has been burnt; these are Cantharellus carbonarius and Agaricus (collybia) atratus. Then, again, another pair of fungi, in which sulphur colour prevails, are found growing together on wood. These are Agaricus (hypholoma) fascicularis and Agaricus (flammula) conissans, or, similarly, Agaricus (hypholoma) capnoides and Agaricus (flammula) alnicola. In all these four the coincidence of colour, form, size, mode of growth, and even habitat, is complete. With any one of these, again, may be compared the recently discovered Agaricus (clitocybe) Sadleri, which has white spores. Here we have five yellow species found growing on wood, and so like each other that an ordinary observer would consider them all as the same species, not taking the colour of the spores into account. There is, moreover, a small agaric, which is known to the majority of mycologists on account of its strong odour of stinking fish (Agaricus cucumis). It grows on the ground, and upon fragments of wood, and has red-brown spores. Yet there is an imitator in a small fungus with white spores, found in just the same localities, with the identical fishy odour. According to all authority and experience the difference in the colour of the spores is not a mere difference of species, but indicates quite a separate and distinct group of species.
We might also indicate as further removed from each other such species as Agaricus (tricholoma) nudus, a handsome violet species, which when well grown is scarce to be distinguished from Cortinarius violaceus, except that in the former the spores are white, and in the latter rusty.
Taking a still wider range we encounter equally startling resemblances between widely separated groups, such as the whole hypogeous Gasteromycetes, which in form, size, odour, habit, and all save fructification imitate the truffles (Tuberaceae). Or, opposing certain genera we have in Podaxon a resemblance to Coprinus, and Hypolyssus might be mistaken for an immature Crucibulum. The larger species of Peziza sometimes approach in habit Craterellus. And in Cyphella, with its naked spores, every feature besides corresponds with the small Pezizae, some being like the section Hymenoscypha, others that of Dasyscypha, and others Mollisia.
Comparing fungi with other cryptogamia, the gelatinous species of Tremella are just like such algae as Nostoc. In lichens the species of Lecidea approximate so closely that only experts can distinguish them from Patellaria amongst fungi. Awomyces amongst lichens imitates Stilbum in fungi, whilst the graphideous lichens seem to coalesce almost with Hysteria, and Platygrapha with Stictis.
Already our comparisons are too technical, and we must rest content with thus much allusion to a subject which presupposes too much practical knowledge for a popular volume. We may, nevertheless, urge that amongst the lower order of plants there are coincidences as striking as those instanced in flowering plants. Whatever the interpretation may be, the facts are worthy of remembrance, since we may hereafter, subject to a wider experience, suggest reasons which would now be regarded as premature.
In bringing this interesting subject to a conclusion we may briefly allude to certain fancied resemblances which are occasionally met with, reminding us strongly of members of the animal kingdom. Certain fruits and seeds are supposed to resemble beetles, bugs, & \c., and some flowers to mimic bees, flies, and butterflies. In passing we have alluded to some of these, and shall now rest content with reference to the snake nut of Demerara. This fruit was discovered and made known by Sir Robert Schomburgk in 1840. "For several years past," he says, "nuts of the size of a walnut were brought down from the interior to Georgetown in Demerara, the kernel of which, when opened, and the membrane which covered it being removed, displayed the striking resemblance to a snake coiled up. There was the head, the mouth, the eyes so complete, that one unacquainted with the fact would have believed them to be an imitation made by human hands, and not a freak of nature. As is often the case with the productions of the interior, the colonists were entirely unacquainted with the mode of growth of the plant which produced these strange nuts. They were generally found after the annual swelling of the Essequibo had subsided along its banks, and for a length of time it was pretended that they grew on a creeper, and from the resemblance of its kernel to a snake it was supposed that it might prove an antidote to snake poison." Subsequently it was found to be the produce of a large tree (Ophiocaryon serpentinum) belonging to the same family as the horse chestnut. Our figure represents a nut cut open, and the kernel exposed (fig. 79).
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fig. 79.—Snake nut (Ophiocaryon serpentinum) cut open.
As in some sort to counterbalance a too rigid application of utilitarianism to forms and modifications of plant structure, especially such as relate to the subject of this chapter, we shall end with a quotation from Mr. A. W. Bennett. He says, "I cannot myself get away from the conclusion that we must attribute the tendency to variation which is admitted to be the material on which natural selection works, to some inherent force belonging of necessity to the functions of life, whether animal or vegetable, which is independent of, and in some sense superior to, the forces that govern the inorganic world. Above all, we are compelled to recur to the pre-Darwinian doctrine of Design; and to believe that nature has some general purpose in the different modes in which life is manifested, a purpose not in all cases for the immediate advantage of the individual species, but in furtherance of some design of general harmony which it may take centuries of unwearied observation and laborious toil before we discover the key by which we may be able to unlock it."
CHAPTER XVI
GIANTS.
"THERE were giants in those days" scarcely includes those of the vegetable world, for the facts which relate to the most gigantic of plant productions are of recent date. Under the term "giant" we do not purpose to include unusual developments of individuals, but to refer to species, of which large dimensions is an attribute. Large oaks, large elms, large forest trees of various kinds are enumerated in all books of forestry, and these have their own interest, but not the same interest as that which attaches to plants which are normally of extraordinary size. Literally, then, we have to deal with vegetable Titans, with "mammoth" trees, and gigantic flowers, commonly attaining dimensions far in excess of ordinary trees and flowers; their claim to notice being their normally unusual size.
It was for some time supposed that the largest of all known trees were the conifers of the western side of the North American continent. The trees known to Englishmen as Wellingtonia and to Americans as Sequoia were, up to a recent date, regarded as the mammoth trees. This supremacy is now broken down in favour of the "big trees" of Australia, although it must be confessed that it is very difficult to determine what are the reliable dimensions of trees recorded in both countries.