HISTORY OF THE GROWTH OF A TREE. 



121 



more cheaply than in any other. Rough 

 or rubble stone wall, covered externally 

 with ivy, or the Virginia creeper, are far 

 more pleasing than the smoothest and rich- 

 est carpeting ; and a church built in this 

 real and solid manner will stand for ages, 



and, with the lapse of time, grow constantly 

 dearer to all who enter it, while wooden 

 churches only grow old to grow more rick- 

 etty, and are too frail and temporary to in- 

 spire respect by their permanence, or vene- 

 ration by their antiquity. 



THE HISTORY OF THE GROWTH OF A TREE. 



BY PROFESSOR LINDLEY. 



[We extract the following interesting phy- 

 siological description of the growth of a 

 tree, from the new edition of Lindley's In- 

 troduction to Botany, — a work of inestima- 

 ble value to the student in this department 

 of science. It will be difficult for such of 

 our readers as are interested in the nature 

 of vital action, and the laws of vegetable 

 growth, to obtain a more definite idea of 

 their general operation than by carefully 

 perusing this extract. Ed.] 



I. If we place a seed (that of an apple, 

 for instance,) in earth at the temperature 

 of 32° Fahr., it will remain inactive till it 

 finally decays. But if it is placed in moist 

 earth some degrees above 32°, and screened 

 from the action of light, its integument 

 gradually imbibes moisture and swells ; the 

 tissue is softened, and acquires the capabi- 

 lity of stretching ; the water is decomposed, 

 and a part of its oxygen, combining with 

 the carbon of the seed, forms carbonic acid, 

 which is expelled ; nutritious food for the 

 young parts is prepared by the conversion 

 of starch into sugar ; and the vital action 

 of the embryo commences. It lengthens 

 downwards by the radicle, and upwards by 

 the cotyledons ; the former penetrating the 

 soil, the latter elevating themselves above 

 it, acquiring a green colour by the decom- 

 position of the carbonic aeid they absorb 

 from the earth and atmosphere, and un- 

 folding in the form of two opposite round- 

 ish leaves. This is the first stage of vege- 

 tation ; the young plant consists of little 

 more than cellular tissue; only an imper- 



Vol, iv. 11 



feet development of vascular and fibrous 

 tissue being discoverable, in the form of a 

 sort of cylinder, lying just in the centre. 

 The part within the cylinder, at its upper 

 end, is now the pith, without it the bark; 

 while the cylinder itself is the preparation 

 for the medullary sheath, and consists of 

 vertical tubes passing through and sepa- 

 rated by cellular tissue. 



The young root is now lengthened at its 

 point, and absorbing from the earth its nu- 

 triment, which passes up to the summit of 

 the plant by the cellular substance, and is, 

 in part, impelled into the cotyledons, where 

 it is aerated and evaporated, but chiefly 

 urged upwards against the growing point or 

 plumule. 



II. Forced onwards by the current of 

 sap, which is continually impelled upwards 

 from the root, the plumule next ascends in 

 the form of a little twig, at the same time 

 sending downwards, in the centre of the 

 radicle, the earliest portion of wood that is 

 deposited, and compelling the root to emit 

 little ramifications ; and simultaneously the 

 process of lignification is going on in all 

 the tissue, by the deposit of a peculiar se- 

 cretion in layers within the cells and tubes. 



Previously to the elongation of the plu- 

 mule, its point has acquired the rudimenta- 

 ry state of a leaf: this latter continues to 

 develope as the plumule elongates, until, 

 when the first internode of the latter ceases 

 to lengthen, the leaf has actually arrived 

 at its complete formation. When fully 

 grown it repeats in a much more perfect 

 manner the functions previously performed 

 by the cotyledons: it aerates the sap that 

 it receives, and returns the superfluous por- 



