ORGANIC STRUCTURE. 



plant or slender body within their reach. This is a 

 curious and unaccountable property. If all twining 

 plants revolved in the same direction, something like 

 a rational reason might be assigned as the cause; but, 

 as some turn to the right and others to the left, it is 

 obvious no extraneous agent can affect vegetation so 

 as to produce contrary motions. It appears, therefore, 

 that this tortive action results from a constitutional 

 arrangement of the fibres of the stem, which may be 

 supposed to be conjointly and spirally disposed round 

 the pith or axis, and which, as they are elongated, 

 continue to revolve by their tendency to become 

 straight, while they are lengthened out. We see, at 

 the same instant, an advancing and an involving or 

 retrovolvant action of the stem ; and the only expla- 

 nation of the phenomenon we can give is, that all 

 twining plants, having their system of stem fibres 

 coiled from right to left, turn to the right ; and those 

 whose fibres incline from left to right, turn to the left 

 during their growth. All this is assumed as a 

 probable theory rather than a demonstrated fact ; for 

 it must be confessed that, except the twisted or 

 spiral position of the furrows on the surface, dissec- 

 tions of these stems have yielded no corroboration of 

 the opinion. The spirally lying position of the fibrous 

 structure of stems, and the spiral vessels found in 

 young shoots, roots, petals of flowers, &c. are 

 evidently organs having a mechanical action to assist 

 in the elongation or expansion of the cellular tissue 

 in which they lie imbedded. In this character these 



