the confounding together in thought and language of totally
different things which came under consideration, the so-called
thickening-ring, in which the first vascular bundles were supposed to originate close under the summit of the stem, being
confounded with the cambium of true woody plants which is
formed at a much later period, and both of them again with the
very late-formed meristem-layer in arborescent Liliaceae, in
which new vascular bundles are continually being produced
and cause a peculiar enlargement of the stem[1]. Sanio's treatise
first removed this confusion of ideas, which appears in von
Mohl himself to some extent even in 1858, by sharply distinguishing the thickening-ring beneath the point of the stem,
in which the vascular bundles begin to be formed, from the
true cambium, which is formed at a later time in and between
the vascular bundles, and produces the secondary layers of
wood and rind; Sanio also occupied himself with submitting
the various elements of the wood to a more careful examination, and with giving them a better classification and terminology. The peculiar instance of secondary growth in thickness in the arborescent Liliaceae, which had long been known and had helped to mislead von Mohl and Schacht, was fully explained for the first time by A. Millardet in 1865. The later works of Nägeli, Radlkofer, Eichler and others on abnormal wood-formations contributed materially to enlarge the knowledge
of normal growth also; but these coming after 1860, and
Hanstein's later investigations into the differentiation of tissues at the end of the stem in Phanerogams, do not fall within the limits of our history.
4. Nageli's Theory of Molecular Structure and of Growth by Intussusception.
This theory, the importance of which to the further development of phytotomy and vegetable physiology has been already
- ↑ See Sachs, 'Lehrbuch der Botanik,' ed. 4 (1874), p. 129 (p. 128 of 2nd English edition).
