LIFE. 



155 



tegration of its tissues; or it may be preserved 

 in consequence of the absence of those agents 

 which ordinarily excite decomposition. The 

 occasional suspension of vital action from a 

 change in the organism itself, appears usually 

 to result from a general law of periodicity, 

 whicli affects, more or less, all organised 

 beings, producing the phenomena of sleep, 

 hybernation, &c.; but it may also arise from 

 particular causes operating within the system, 

 as in syncope. Each of these cases will now 

 be separately considered. 



Dormant vitality of seeds, eggs, 4'<"- The 

 condition of organised beings of which we have 

 first to treat that in which vital action is sus- 

 pended from the absence of the stimuli ne- 

 cessary to maintain it, and vitality never- 

 theless preserved is manifested in the most 

 remarkable manner by the reproductive germs 

 which are periodically separated from plants 

 and animals, and which are endowed with the 

 power of developing themselves into new indi- 

 viduals when the requisite conditions are sup- 

 plied to them. In the lowest classes of each 

 kingdom, it would appear that these germs are 

 liberated from the parent unprovided with any 

 means for the continuance of their development ; 

 and that from the first, therefore, they rely upon 

 the surrounding elements for all the conditions 

 of their active existence. It is beautifully pro- 

 vided that, in proportion to the probable defi- 

 ciency of some of these, should be the tenacity 

 with which the apparently lifeless germs re- 

 tain their vitality. The sporules of the fungi, 

 which can only subsist on decaying organised 

 matter, seem universally diffused through the 

 atmosphere, and ready to vegetate with the 

 most extraordinary rapidity whenever a fitting- 

 nidus is afforded for their development. This, 

 at least, appears the only feasible mode of ex- 

 plaining their appearance in the forms of mould, 

 mildew, &c. on all decaying surfaces ; and 

 that there is no improbability in the suppo- 

 sition itself is shown by the estimate of Fries, 

 who states that a single individual of reti- 

 cularia maxima will emit above 10,000,000 of 

 these germs, so minute as when collected to 

 be scarcely visible to the naked eye, rather re- 

 sembling thin smoke, and so light as to be 

 wafted by every movement of the atmosphere, 

 so that, he remarks, " it is difficult to conceive 

 a place from which they can be excluded." 

 It seems more than probable that in a similar 

 manner is to be explained the appearance of 

 infusorial animalcules in all situations adapted 

 to their existence ; and that their germs are 

 constantly and universally diffused through the 

 air, ready to commence the active exercise of 

 their dormant properties whenever they meet 

 with the stimuli to their development afforded 

 by warmth, moisture, and decomposing organic, 

 matter.* 



We have no means of ascertaining the 

 length of time during which this dormant vi- 

 tality may be preserved. It would be difficult 

 to assign a limit to it, since it is scarcely con- 

 ceivable that any change can occur in the struc- 



* For an important experiment on this subject 

 recently performed by Schultz, see Edinburgh Phi- 

 losophical Journal, Oct. 1837. 



ture of these minute desiccated points which 

 they do not undergo during the first few 

 hours of their aerial residence ; and we have 

 no reason to believe that vitality can be de- 

 stroyed without change of structure. With re- 

 gard to the seeds of phanerogamic plants, we 

 have more certain evidence, and this of a very 

 interesting character. It is to be remarked, 

 however, that in them, as in the eggs of 

 higher animals, there is, besides the germ it- 

 self, a reservoir of nutriment supplied by the 

 parent, which enables the germ to continue its 

 development up to the point at which it be- 

 comes fit to maintain its own existence, with- 

 out any other than the ordinary assistance of 

 vital stimuli. The germination of a seed, for 

 example, requires only warmth, moisture, and 

 the access of air, and is further accelerated by 

 the absence of light ; and the hatching of an 

 egg is dependent only on a temperature more or 

 less elevated and the presence of air. Hence 

 the necessity for so great a tenacity of vitality 

 as that possessed by the germs of the simpler 

 classes does not exist, and although under 

 favourable circumstances the vitality of seeds 

 may be prolonged for an almost indefinite 

 period, they are more susceptible of the inju- 

 rious influence of external agents, and their 

 fertility is destroyed by changes of condition 

 which would have no effect in the former case ; 

 whilst the eggs of animals appear still less tena- 

 cious of vitality, although in a few instances 

 capable of retaining it for some time, even under 

 considerable disadvantages, as will be presently 

 noticed. 



The seeds of most plants which inhabit tem- 

 perate climates are 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 



