generating tissue, the original component of every young organ,
he named primary meristem as distinguished from prosenchymatous generating tissue, which is differentiated in the
form of strands and layers, and received from him the general
name of cambium; this was certainly not a happy distinction,
because Nägeli's cambium by no means consists entirely of
prosenchymatous tissue. By the term secondary meristem
Nägeli designated the tissue-strands and tissue-layers which
are formed between the permanent tissue of older parts. The
cambium he regards as the first product of the primary meristem.
The second chief form, permanent tissue, he divides into two
classes, not according to the form of the cells or physiological
relations, but according to its origin ; all permanent tissue,
which is derived immediately from primary meristem, is
protenchyma, all that comes directly or indirectly from cambium is epenchyma. And since the tissue-strands, till then
known as vascular bundles, do not contain vessels only but
always fibrous elements also, as Bernhardi had shown in 1805,
Nägeli thought that they should therefore be called fibrovascular
strands. If it cannot be denied that the obvious distinction
between epidermal and other tissue did not find suitable
expression in this classification, and though other points of
view may at the present day be proposed for the genetic
arrangement of tissues, yet Nägeli's classification and terminology have the merit of having for the first time exhibited
the general histology of plants on comprehensive and genetic
principles. It contributed materially to impart a better under-
standing of the collective structure of plants.
The vascular bundles or fibrovascular strands especially demanded further investigation of the genetic and morphological kind; for a correct insight into the origin and subsequent transformation of this tissue-system is as important for phytotomy as a similar knowledge with respect to the bony system in vertebrate animals is for zootomy. But a knowledge of the vascular bundles and their course in the stem has a special im-
