ART. II. On the Functions of the Spiral Vessels and the Pith in 

 Vegetables. By William Colvill^ Esq. 



It has been well remarked by Keith, that, notwithstanding 

 " all the elucidation that has been thrown on the subject, the func- 

 tion of the spiral tubes is as much involved in obscurity as ever." * 

 Phytologists appear to be divided betwixt the two opinions, whether 

 they be sap- vessels or air-vessels. It may be deemed a bold step, 

 then, for an individual, scarcely known in the field of science, to ad- 

 vance the opinion that they are neither, but are the peculiar organs 

 by means of which the longitudinal growth of the plant is effected. 

 Such, however, is the conclusion at which I have arrived after a 

 careful investigation. 



Without attempting directly to combat the opinion advanced 

 by others, I may be permitted to remark that, if the spiral tubes or 

 tracheae be sap-vessels, it is remarkable that their existence cannot 

 be traced in the root,t by the medium of which plants are supplied 

 with sap. On the other hand, if they be air-vessels, is it not equal- 

 ly remarkable that they are not to be found either in the root or 

 among the ligneous layers of the stem ? % 



Before entering upon the investigation of the functions of the 

 spiral vessels, it will be proper to ascertain those parts of vegetables 

 in which they are to be found. These it will be sufficient at pre- 

 sent merely to indicate. They are the stem, and in woody plants 

 always surrounding the pith ; the leaf-stalk, mid-rib, and ramifica- 

 tions of leaves ; the flower-stalk, the calyx, the stamens, the pointal, 

 and the other parts of the flower, and the cotyledons and plumula 

 of the seed. Such being their situation, let us proceed to the con- 

 sideration of their functions. As conservatory organs, they must 

 be destined either to promote the growth or the preservation of the 

 plant. II Permit us, in the first place, to inquire how far they are 

 essential to the preservation of the plant. 



The operation of grafting demonstrates that it is not essential to 

 the existence of the scion that a continuity of spiral vessels be pre- 

 served through the plant ; for in this operation, that continuity is 

 completely broken, and both the stock and scion nevertheless con- 

 tinue to flourish. But not only may the continuity of the spiral 

 vessels be broken with impunity, but the vessels themselves may 

 be wholly removed from the stem without injury either to its exis- 



• Keith's Physiological Botany, B. iv. C. 3. Sec. 2. 



•j- Library of Useful Knowledge, Veg. Phys. pp. 13, 14. ; Keith, B. iii. 

 C. 3. Sec. 2. ; De Candolle, Vol. I. B. i. C. 3. Art. 2. 



X De Candolle, Organographie Vegetale, Vol. I. B. i. C. 3. Art. 2. ; Lib. of 

 Useful Knowledge, p. 6. ; Smith's Introduction to Botany, C. 8. ; Keith, B. iv. 

 C. 3. Sec. 2. ; De CandoUe, Vol. I. p. 38. ; Knight, Philosophical Transac- 

 tions. 



II Lib. of Useful Knowledge, Veg. Phys. p. L ' ' 



