22 Mr D. Don p7i Spiral Vessels in the Vegetable ^Structure. 



been led to these remarks by the ingenious observations of Mr 

 Lindley in a late number of the Botanical Register, on the 

 structure of the seeds of Collomia, which he has shewn to be 

 enveloped by a plexus of spiral vessels. These vessels in Pole- 

 moniacece appear to be analogous to the coma or pappus with 

 which the seeds of certain Bignaniacece, Apocineoe^ and Malvor- 

 ceoe are furnished ; but further observations seem necessary be- 

 fore we can conclude that they are true spiral vessels. Spiral 

 vessels are most abundant in the stems of Urtica nivea, Ceiir- 

 taurea atro-purpureay Heliopsis Icevisy Helianthus altissimus. 

 Aster Novi Belgii and salicifblius, in all which they are dis- 

 tinctly visible to the naked eye, and on this account these 

 plants maybe recommended as furnishing the most beautiful ex- 

 amples of spiral vessels for the student in botany. The stalks, 

 when torn gently in a longitudinal direction, and a small peg 

 placed in the top of the fissure, exhibit the spiral vessels much 

 more distinctly than by a transverse fracture. Sometimes the 

 folds of these vessels were found seated in the pith, both in Ma- 

 lope trifida and Heliopsis lavis, biit they were easily traced to 

 their origin among the woody fibres. No trace of them has 

 been found in the outer bark, but they abound in the liber 

 or inner bark of Pinus, as well as in the albumen. I have ne- 

 ver been able to detect them, however, in the leaves of this ge- 

 nus, nor of Podocarpus, and they appear to be of rare occur- 

 rence in the leaves of evergreen trees in general. The stems 

 and leaves of Polejiioniacete, Iridea, and Malvacea are also 

 abundantly supplied with spiral vessels ; but perhaps in no fa- 

 mily do they abound so much as in the Compositce. They are 

 rare in Cruci/erce, Leguminosa, and Gentianea. 



I have frequently remarked, on detaching the spiral vessels 

 from the young vigorous shoots of herbaceous plants, that they 

 became violently agitated. The motion continued for som,e se- 

 conds, and appeared to me to be attributable to the effect of the 

 living principle, analogous to what takes place in the animal 

 economy, and not to a mere mechanical action. 



While holding between my fingers a small segment of the 

 bark of Urtica nivea, which I had just then detached from the 

 living stem, my attention was instantly attracted tp the peculiar 

 spiral motion which it exhibited. The experiment was repeated 

 several times successively with other pieces of the bark, and the 



