The seeds of most plants which inhabit tem perate climates arc adapted to remain dormant during the winter, and may be preserved in dry air and moderate temperature for a consi derable time. Some of those which had been kept in the Herbarium of Tournefort for up wards of a century were found to have pre served their fertility. But with regard to those which are brought from tropical climates there is greater uncertainty, and unless they have been carefully excluded from the contact of air and from variations of temperature, a large pro portion are usually unproductive. Cases are of no unfrequent occurrence in which ground that has been turned up spontaneously produces plants dissimilar to any in their neighbourhood. There is no doubt that in some of these the seed is conveyed by the wind, and becomes developed in spots .which afford congenial soil, in the same manner as the germs of fungi and infusoria. Thus it is commonly ob served that clover is ready to spring up on soils which have been rendered alkaline by the strewing of wood-ashes, or the burning of weeds ; and it is stated by Professor Graham that after any hill-pasture in Scotland has been laid dry and limed and the surface broken, white clover always makes its appearance. But there are many authentic facts which can only be explained on the supposition that the seeds of the newly-appearing plants have lain for a long period imbedded in the soil, at such a distance from the surface as to prevent the access of air and moisture, and that, retaining their vitality under these circumstances, they have been excited to germination when at last exposed to the requisite conditions.* Most physiologists, at least, are content to adopt this explanation, seeing that it is con formable to what is otherwise known of the persistence of vitality in seeds ; but it has been recently maintained that in such instances a spontaneous production lakes places, similar to that which many philosophers have supposed to occur among the lower tribes of organised beings.t This is not the place to discuss such a theory, of which it would not perhaps be very difficult to show the absurdity ; but the following case furnishes, we apprehend, a very satisfactory proof that seeds may preserve their vitality for an unlimited time, when the ex ternal conditions are such as to prevent either the active exercise of their properties or the disorganisation of their structure. " I have now before me," says Professor Lindley4 " three plants of raspberries wli ich have been raised in the gardens of the I horticultural Society, from seeds taken from the stomach of a man, whose skele ton was found thirty feet below the surface of the earth, at the bottom of a barrow which was opened near Dorchester. He had been buried with some coins of the Emperor Hadrian, and it is probable, therefore, that the seeds were six teen or seventeen hundred years old." In regard to eggs, no such examples are, we believe, on record ; nevertheless, there are some tribes of animals whose eggs are capable of being preserved for a considerable length of time, and of undergoing very severe treatment without loss of their vitality. Most insects de posit their eggs sufficiently early in the summer for the larvae to be hatched and attain their full growth before the autumn deprives them of their supply of food, and these pass the winter in the pupa state. But there are some which do not begin to lay until the activity of vegetation has nearly ceased, and their eggs remain undeveloped until the ensuing spring arouses both the animal and vegetable creation into life. The curious instincts which lead these insects to choose secure places for the de position of their eggs, and to use other means of protecting them against cold and moisture, are described by Mr. Eirhy ;§ and the same author points out the beautiful correspondence between the temperature required for the de velopment of the buds of the plant and of the larva that prey upon them. It has been men tioned in a former articlell that the eggs of the slug are capable of enduring a temperature of 40°, and of being completely desiccated, with out losing their fertility ; and it can scarcely be doubted, therefore, that these might preserve their vitality like the seeds of plants for an un limited period, if neither aroused into activity nor disorganised by decomposing agents.
It will scarcely be denied that the agents which are known to destroy the vitality of seeds and eggs are such as are calculated to produce important changes in their structure and composition, even though these be of a kind inappreciable by our present means of re search. Thus most seeds are killed by a tem
perature of which is that at which rup ture of the vesicles of fecula takes place, and the application of heat sufficient to destroy the vitality of an egg coagulates its albumen. An electric shock is well known to be a powerful means of instantaneously extinguishing the vital properties of eggs or seeds ; and although tl precise alterations which it effects in the stru ture or composition of their parts is not under stood, it cannot be doubted that important or ganic changes are produced by so powerful an agent. Cold, in like manner, probably acts injuriously on most eggs and seeds as upon plants, by causing the rupture of the cells of their tissues through the expansion of the con tained fluids in the act of freezing. We do not mean to say that other changes are not also produced by such agents, but we mention these as evidences of the position with which we started—that vitality is not destroyed by the influence of external agents without a structural change of some kind being induced by their operation.
But it is not during their embryo state merely, that the vital actions of living beings may be suspended by the deficiency of external stimuli, and yet their vitality be preserved. Both the vegetable and animal kingdoms afford numerous examples of such an occurrence at all periods of existence, especially among their lower tribes. Mosses, for instance, often ap pear completely desiccated in dry weather, and seem as if dead ; whilst, on the application of moisture, they revive in all their pristine beauty. The curious Lycopodium of Peru exhibits thi torpor in a still more remarkable mann 'When desiccated by drought, it folds in i leaves and contracts its roots so as to form a ball, which, apparently quite devoid of anima tion, is driven hither and thither by the wind ; as soon, however, as it reaches a moist situa tion, it sends down its roots into the soil, and unfolds to the atmosphere its leaves, which, from a dingy brown, speedily change to th bright green of active vegetation. The ro of Jericho is the subject of similar transform< tions. Instances exactly parallel are furnished by the animal kingdom. The common wheel animalcule is one of the most being capable of desiccation so complete as splinter if touched with the point of a needle, and still preserving its vitality so as to revive when moistened.* In animals reduced to a state of torpidity by cold, some vital action usually continues ; and such cases cannot therefore be adduced under the present head. But instances are by no means rare in which the whole body has been frozen, and vital action has of course been completely suspended, yet without the destruction of the power of renew ing them under more favourable circumstances. Lister first noticed that he had found caterpil lars so frozen, that when dropped into a glass they chinked like stones, but nevertheless re vived ; and this statement has been confirmed by Bonnet and others. The Papilio Brassice has been produced from a larva which had been exposed to a frost of 0° Fahr., and which had become a lump of ice. Fishes are occasion ally found imbedded in the ice of arctic seas; and some of these revive when thawed. This tenacity of life appears greater, however, in the species which are confined to shallow lakes or ponds, and which have not the power, there fore, of escaping from the effects of cold. This is perhaps the proper place to mention those undoubted cases in which insects have been apparently killed by immersion in water or spirit, continued for a long period, and have yet revived on exposure to the air and sun.
Without multiplying facts, then, it may be safely affirmed that many organised beings may retain their vital properties, in some in stances to an unlimited duration, while all vital activity or life is completely suspended, through the absence of the stimuli necessary to main tain it ; and that this preservation of vitality bears so close a relation to the resistance offered, by the structure and composition of the sub stance possessing it, to the influence of disin tegrating agents, that it may reasonably be considered as a result of the maintenance of its normal constitution. The physiologist is not yet in a condition to explain those diffe rences in structure and composition which enablesome organisms to offer a much greater re sistance to such injurious influences than others ; but he considers himself entitled to assume that midi, exist in all, since there are many instances in which he is able to detect them.