5!^6 Miscellaneous » 



On Circulation in Plants. By A. Trecul. (Second Part*.) 



During the life of a plant all the liquids are in motion in each of 

 the utricles of which it is composed, either to carry into these 

 the elements necessary for their growth, or for the formation of the 

 amylaceous, saccharine or albuminoid principles, &c., to which they 

 give origin, or to remove from them those substances which have 

 become useless and which require to be eliminated, or those which 

 have to be carried to other parts of the plant to serve for the multi- 

 plication of the cells and the growth of the individual. It is this 

 general movement that constitutes the circulation ; but this name is 

 usually given to definite currents, more perceptible than this general 

 intracellular movement, which traverse the plant through its whole 

 length from top to bottom and from the bottom to the top. 



It is to this double current that I give the name of the great cir- 

 culation, I have also indicated the venous circulationy which takes 

 place, as I have stated, in the laticiferous vessels. 



The great circulation is observed in all vascular plants ; but the 

 laticiferous vessels have not yet been detected in all plants which 

 possess vessels. 



The great circulation therefore consists of an ascending current of 

 the sap, and of a descending current. Let us first of all take the 

 former into consideration. It takes place in the vessels which 

 receive and elaborate the juices drawn from the soil by the roots. 

 When this ascent commences, all the cells are at work. The nutri- 

 tive substances which they contain arrange themselves by assimi- 

 lation. Starch, dissolved no doubt by diastase, and converted into 

 sugar, as has been shown by MM. Pay en and Persoz, is carried to 

 the parts where the cellular multiplication is to take place. The 

 starch of the base of the buds serves for the alimentation of the 

 latter ; that of the bark passes into the internal cells of that part of 

 the plant, which very probably also receives some by the medullary 

 rays. It is under the influence of these nutritive materials that the 

 increase in diameter by the multiplication of cells commences. This 

 multiplication at starting really takes place without the aid of the 

 sap elaborated by the leaves, for in many of our trees the layer of 

 young cells (generative layer, also called cambium) acquires a con- 

 siderable thickness before the appearance of the leaves. 



These first phsenomena make their appearance with the ascent of 

 the sap. This, in rising, undergoes an elaboration, with which I am 

 not sufficiently acquainted to speak of it at greater length ; I shall 

 content myself with indicating the beautiful experiments of M. Biot, 

 which have shown us the changes which sugar undergoes during the 

 progress of this sap. During its ascent it already contains assimilable 

 principles which may assist in the nutrition of the leaves and buds 

 (in which the spiral vessels make their appearance from below up- 

 wards) ; but in the spring these buds are indebted for their first 

 development especially to the alimentary substances amassed in the 

 jieighbouring cells, 



t ae§ Aw^ls, Pp(5, 1857, p. 467, 



