Page:History of botany (Sachs; Garnsey).djvu/292

272 transverse bands on false spiral vessels (scalariform ducts) and the pits of dotted vessels are formed on the walls of membranous fibre-tubes; in like manner he derives true spiral vessels from long thin-walled cells, on whose inner surface the spiral band is formed, and well compares the members of young spiral vessels with the elaters of the Jungermannieae. Here then we find the first more definite indications of a theory of growth in thickness of cell-walls, which, like the theory of the origin of vessels from rows of cells, was afterwards developed by von Mohl and laid on better foundations. At the close of the essay the histology of the Cryptogams, Monocotyledons and Dicotyledons is compared, and the subject is better and more perspicuously handled than in the corresponding chapters of his competitors.

Though Treviranus' account of vegetable tissues was on the whole weak as far as concerns the history of development, yet recognised in him the most dangerous opponent of his own theory, and addressed a public letter to him and not to his other German antagonists, Sprengel, Link and Rudolphi, in defence of the views he had formerly expressed. This letter is the first part of a larger work which appeared in 1808,