B O T A N Y. 



gy- 



Light 



Preserva- 

 tion of 

 ceils. 



Vf etable distinguishes by the name of imbibition ; but after- 

 Physiolo- war( ]s a living action takes place in the vessels, and 

 the fluid is circulated through the cotyledons, and is 

 finally conveyed to the embryo plant. M. Scnnebier 

 has fully established the existence of this last fact. 

 Light has been supposed by Sennebier and Michelotti 

 to be injurious to germination ; but de Saussure seems 

 to have established, that the injurious effect is ow- 

 ing to the accumulation of heat, which is insepara- 

 ble from the solar rays. 



It is a valuable fact, that many seeds will keep fcr 

 a very long period, when deprived of moisture: the 

 period, indeed, as far as we can ascertain, seems to 

 be unlimited. It is stated, on the respectable authority 

 of Ray, that, after the great fire in London in IfifiG, 

 Sisymbriiim irio of Linnasus covered the walls of 

 some buildings which had been burnt. From tluir 

 situation, they must have lain for at least some hun- 

 dred years. It* is remarkable, that this plant was 

 very scarce in London previous to the fire. 



Gerardin reports, on the authority of M- Dcsfon- 

 taines, that a similar event occurred at Versailles 

 when an old tower was pulled down. The same au- 

 thor mentions another fact which came under his own- 

 observation, in the " Jardin dcs Plantes," and which 

 confirms the statements already made of the power 

 which some seeds possess of retaining this vital prin- 

 ciple for a considerable time. " In rooting up, (says 

 he) some years ago, in the garden of plants, an old 

 tree, the species of which could not be discovered, a 

 circular trench was made by throwing aside the earth 

 which came up with it. It was remarked, that in 

 this earth there were different kinds of seeds which 

 were well preserved ; (they had no doubt been there, 

 Tis it were in a depot, since the time when the hole 

 in which the tree was planted had been filled up 

 with earth in which they were ;) they were sown, 

 they germinated, their stems were developed, and they 

 produced flowers and fruit." 



Dr Smith also states, from Mr Fairbairn of Chelsea, 

 that frequently species long lost have been recovered 

 by digging deep in old established botanic gardens. 

 Humboldt ascertained the following curious and valu- 

 able fact connected with germination, that seeds which 

 would not germinate under ordinary circumstances, 

 very readily did so after immersion in oxymuriatic acid 

 fcr about six or seven hours. As this acid is not always 

 io be had, and as it may be of considerable import- 

 ance to the practical gardener, we shall here insert 

 the formula recommended by him, and given by 

 Willdenow, for its extemporaneous preparation. A 

 cubic inch, or about an ounce of water, a tea-spoonful 

 of common muriatic acid or spirits ef salt, two tea- 

 spoonfuls of black oxide of manganese, must be 

 well mixed together, and the seeds must be digested 

 in this mixture at a temperature of from 18 to 30 

 Fahrenheit. As soon as the corcle appears, it is pro- 

 per to take the seeds out, and to sow them in earth. 

 Seeds thrive also in compressed air, in ammonia ; 

 but not in any fluid of which oxygen is not a con- 

 stituent. 



Some seeds have a wonderful power of preserving 

 their vital principle ; while others lose it almost im- 

 mediately after turning ripe, unless planted. Mr 

 .Salisbury has established in a satisfactory man- 

 ner, that seeds cannot be kept too warm, pro- 



Of rost 

 and pic 

 mula. 



vided the nature of the oily juices be not altered by 

 it. Gardeners keep melon and cucumber seeds for 

 a few years, when they wish to diminish the luxuri- 

 ance of their plants, and to obtain a greater profusion 

 of blossoms and fruit. That this effect is produced 

 is unquestioned, though it is not equally certain that 

 Dr Darwin's solution of it is correct. The doctor 

 supposed, that the cotyledons receive such injury 

 from keeping, that they lose the power of nourishing 

 the young plant, which consequently remains stunted 

 during the whole of its existence. 



Physiologists have remarked, with admiration, that Directi 

 the plutmila always ascends, and that the rostel always 

 descends. This curious fact has been variously ex- 

 plained ; and Dr Darwin, with his usual ingenuity 

 and boldness, supposed that the rostel is chiefly 

 stimulated by moisture, and the plumula by air, 

 and that each affected its peculiar stimulus. Whe- 

 ther that be the true explanation or not is of very lit- 

 tle importance ; but the fact is fully established by 

 the experiments of Hunter, Duhamel, and Knight. 

 Dr Smith is of opinion, that if soils were homoge- 

 neous, all roots would be perfectly perpendicular. 

 When the rostel has made some progress, (which it 

 seems to do, not by the expansion of parts already 

 formed, but by the gradual addition to its extremity 

 of a fluid which is transmitted from the corcle, and 

 which gradually accumulates at that extremity,) the 

 cotyledons swell, burst, and are carried up with the 

 ascending stem, and for a time perform the functions 

 of leave?. Such is the general process in dicotyledo- 

 nous plants : it is different in the mcnocotyledonous, 

 to which grasses, palms, and the orchides belong. In 

 these plants the cotyledon never appears above ground, 

 so that many are induced to believe them devoid of 

 this organ. Dr Smith is disposed to adhere to the 

 old division. We confess that the facts stated by 

 Willdenow appear to us to carry considerable weight. 



Scheele long ago ascertained, that carbonic acid gas 

 was formed, and that a portion of the oxygen of the 

 atmosphere disappeared during the germination of 

 seeds. The subsequent experiments of Ingenhousz, 

 Gough, Cruikshank, Saussure, and Ellis, have con- 

 firmed those of Scheele, and have fully established, 

 that oxygen gas, either pure or in the state of at- 

 mospheric air, is essential to the germination of seeds ; 

 that it is converted into carbonic acid ; and that the 

 carbonic acid is equal in bulk to the oxygen lost. Mr 

 Ellis has very properly pointed out the absolute ne- 

 cessity for keeping in mind the difference of the action 

 which takes place in seeds without germination, and 

 that with germination ; in the first case a spontaneous 

 decomposition induces the effect ; in the last, it is the 

 result of a living action, and of a subsequent che- 

 mical combination. He argues, and to us his ar- 

 guments appear satisfactory, as no vessels in the 

 seed have been detected proper to the absorption of 

 gaseous fluids, and as there is a parity in the quantities 

 of the oxygen lost and the carbonic acid formed, that 

 it is expedient, at least until farther proof of the con- 

 trary opinion can be advanced, to conclude, that the 

 conversion takes place exteriorly to the substance of 

 the seed, and, consequently, that no absorption of 

 oxygen ever happens. 



A knowledge of these various facts, as well as of 

 the peculiar habits of different seeds, may be of consi- 



Chcmi 

 chaiig< 



