Page:An introduction to physiological and systematical botany (1st edition).djvu/77

 Rh than an entirely new theory of vegetation, by which the real use and functions of the principal organs of plants are now for the first time satisfactorily explained.

In a young branch of a tree or shrub, or in the stem of an herbaceous plant, are found, ranged round the centre or pith, a number of longitudinal tubes or vessels, of a much more firm texture than the adjacent parts, and when examined minutely, these vessels often appear to be constructed with a spiral coat. This may be seen in the young twigs and leaf-stalks of Elder, Syringa, and many other shrubs, as well as in numerous herbaceous plants, as the Peony, and more especially many of the Lily tribe. If a branch or stalk of any of these plants be partly cut through or gently broken, and its divided portions slowly drawn asunder, the spiral coats of their Vessels will unroll, exhibiting a curious spectacle even to the naked eye. In other cases, though the spiral structure exists, its convolutions are scarcely separable at all, or so indeterminate as to be only marked by an interrupted line of perforations or slits, as shown by M. Mirbel. Indeed the very same branches which exhibit