The researches of Hofmeister, Nägeli, Hanstein, Sanio, and
others into the first formation of vascular bundles from the
fundamental tissue of young organs led to important results
for morphology, in so far as it was now for the first time
possible to judge of the morphological value of anatomical
and histological relations. The growth in thickness of woody
plants, a question of primary importance to vegetable physiology, was first made intelligible by the discovery of the mode
of formation of vascular bundles and their true relation to
cambium; Hanstein and Nageli, and afterwards Sanio especially, cleared up the questions connected with growth in
thickness in their main features before and after 1860.
When we pass on to show how the great results above- mentioned were attained, we encounter some difficulties. After 1840 botanical literature multiplied to an extent before unknown; it is from elaborate monographs on single subjects in phytotomy, from some text-books, and especially from smaller essays in botanical periodicals that we must gather an account of the further development of scientific thought. Much as the founding of scientific periodicals has facilitated communication between professed botanists, yet this form of literature makes it more difficult to see the way clearly through the work of earlier periods and to discover the historical connection in the science, not to speak of the harm that usually results from it to young and inexperienced students.
Such being the nature of the sources from which we must draw our information, we shall obtain a better general view of the whole subject if we depart from the practice of former chapters, and follow out the more important questions in their historical development instead of connecting them directly with leading persons. Such a treatment of the subject is indeed suggested by the fact that we are now no longer on
