and of Rural Lnprovement generally^ during 1840. 629 



of the carbonic acid, of which carbon is assimilated, and the 

 oxygen is again restored to the atmosphere. This opinion is 

 certainly not new, but it has scarcely been generally appreciated, 

 in consequence, Liebig considers, of the imperfect knowledge of 

 chemical principles by naturalists, and the want of any decided 

 physiological experiments to determine the point. " Nature," 

 he says, " speaks to us in a peculiar language, in the lan- 

 guage of phenomena ; she answers at all times the questions 

 which are put to her ; and such questions are experiments." 

 On the other hand. Professor Liebig believes that the chief 

 influence exercised by humus on vegetation arises from its 

 being " a continued source of carbonic acid, which it emits 

 slowly. An atmosphere of carbonic acid, formed at the expense 

 of the oxygen of the air, surrounds every particle of decaying 

 humus. The cultivation of land, by stirring and loosening the 

 soil, causes a free and unobstructed access of air. An atmo- 

 sphere of carbonic acid is, therefore, contained in every fertile 

 soil, and is the first and most important food for the young plants 

 which grow in it." A variety of other interesting matter is 

 discussed in this volume: such as the transformations or meta- 

 morphoses which take place in the organs of plants ; the assimi- 

 lation of hydrogen and nitrogen ; the art of culture ; the 

 interchange of crops and manure, &c. Instructions in Garden- 

 ing, for Ladies, by Mrs. Loudon (p. 350.), is by far the best 

 book for grown-up gardening ladies that has ever appeared ; and 

 there is not perhaps another lady in England, or a gentleman 

 either, who could have produced such a work. We state this, 

 because, to have done so, it is necessary for the writer to have 

 been in the very peculiar circumstances of the authoress previous 

 to writing it, viz. to have arrived at maturity before she began to 

 study either gardening or botany. (See the preface to the work, 

 copied in p. 350.) A Pocket Dictionary of Garden Botany, by 

 Mr. Paxton, will be found an exceedingly useful book for ama- 

 teurs. The new Flora of North America (p. 558.) is an admira- 

 ble work, which ought to find its Avay into the library of every 

 botanist ; as should Royle's Illustrations of the Botany of the 

 Himalayan Moimtains (p. 34-8.). Both these books contain 

 descriptions of many hundreds of plants, ligneous and herba- 

 ceous, which are adapted for growing in the open air in this 

 country ; and for that reason they are particularly deserving 

 of the attention of the cultivator. Many of the plants alluded 

 to will be yearly sent home, and references will be continually 

 made to these works, to ascertain their native habits, on which 

 will be grounded the kinds of culture which they require. Kol- 

 lar's Treatise on Insects injurious to Garde?2ers, Foresters, and 

 Farmers is by far the best work of the kind for the practical gar- 

 dener that has ever appeared ; and it is not too much to say that 

 1840. Dec. t t 



