MORPHOLOGY OF TISSUES. 
exist ; here is found a homogenous tissue, the cells of which are all capable of 
division, rich in protoplasm, with thin and smooth walls, and containing no coarse 
granules. This tissue is termed Primary Meristem ; it is a meristem because all 
the cells are capable of division, and primary because it presents the condition out 
of which the different permanent forms of tissue are successively formed by differen- 
tiation (' Proto-meristem ' might perhaps, therefore, be a better term). If the general 
structure of the plant is simple, as in Algae and Characese, the cell-forms arising 
from the primary meristem only differ slightly from one another. If the plant belongs 
to a higher type, as in Vascular Cryptogams and Phanerogams, layers of tissue of 
a different character first originate from the undifferentiated primary meristem which 
proceeds from the growing apex, and in these the different cell-forms of the 
epidermal and fundamental tissues, as well as of the fibro-vascular bundles, finally 
arise by further development, at a still greater distance from the primary meristem. 
The differentiation takes place so gradually, and at such different periods in the 
various layers of the tissue, that it is impossible at any one time to assign a definite 
lower limit to the primary meristem. As growth proceeds at the end of shoots, leaves, 
and roots, lower portions of the primary meristem become gradually transformed 
into permanent tissue ; but the primary meristem is always again renewed by the 
production of new cells close to the apex. Nevertheless whole organs, the apical 
growth of which soon ceases, may at first consist entirely of primary meristem, 
which finally passes over altogether into permanent tissue, so that no primary 
meristem is left. Examples of this are furnished by the development of the 
sporogonium of Muscinese, of the sporangia of Ferns, and even of most leaves 
and fruits of Phanerogams. 
The terminal pordon of an organ with permanent apical growth, consisting 
entirely of primary meristem, is termed the Growing Point or ' Punctum Vege- 
tationis;' not unfrequently (but by no means always) it projects as a conical 
elongation, and is in this case distinguished as the Vegetative Cone or Cone of 
Groivih. 
The production and renewal of the primary meristem commence with the 
cells lying at the apex of the growing point ; and, by the manner in which this 
happens, two extreme cases may be distinguished, which are however united by 
transitional forms. In the one case, the usual one with Cryptogams, though not 
without exception, the whole of the cells of the primary meristem trace their origin 
back to a single mother-cell lying at the apex of the growing point and called 
the Apical Cell. In some Cryptogams, on the other hand, and in Phanerogams, 
there is no single apical cell of this character ; even when a cell lies at the 
ditto, vol. IV. p. 64. — Hanstein, ditto, vol. IV. p. 238. — Geyler, ditto, vol. IV. p. 481. — Müller, 
ditto, vol. V. p. 247. — Rees, ditto, vol. VI. p. 209. — Nägeli und Leitgeb, in Beiträge zur wissen. 
Bot., Heft IV. München 1867. — J. Hanstein, Die Scheitelzellgruppe im Vegetationspunkt der 
Phaneroganien (in the Festschrift der niederrh. Ges. für Natur- und Heilkunde, Bonn ; and 
Monatsübersicht of the same Society, July 5, 1869). — Hofmeister, Bot. Zeitg. 1870, p. 441. — 
Leitgeb, Sitzungsb. der Wiener Akad. 1868 and 1869, and Bot. Zeitg. 1871, nos. 3 and 34. — 
Reinke in Hanstein's Botan. Untersuchungen, Bonn 1871, Heft III. — Russow, Vergleich. Untersuch, 
der Leitbündelkryptogamen, in Mem. de l'Acad. Imp. de St. Petersbourg, 7th ser., vol. XIX. no. i, 
Petersburg 1872. — Warming, Recherches sur la ramification des Phanerogames, in Vidensk. Selsk., 
Skr. 5, Räkke 10, B. i, Copenhagen 1872 (Danish, with French abstract). 
