16 THE SPHAGNACEHZ OR PEAT-MOSSES OF 
nate, obliquely inclined septa, a leaflet is produced composed of a few 
large quadrate parenchym cells filled with a slimy fluid containing 
chlorophyl granules; but with the appearance of the fifth leaflet 
begins the differentiation into two kinds of cells so characteristic of 
the Sphagnacee. 
The leaf becomes marked out into a system of square cells, 
each of which is surrounded by four oblong cells; in the latter 
chlorophyl granules rapidly increase in number and size, while the 
former lose all colouring matter from their contents and keep 
enlarging at the expense of their protoplasm; then the fibres are 
deposited on their internal walls, first as fragmentary rings which 
afterwards coalesce into complete rings or spirals; and lastly, 
small scattered rings appear on the internal surface, the membrane 
enclosed by which becoming resorbed, there result the well-known 
pores or foramina so generally present in the branch leaves of these 
plants, through which it is not uncommon to find infusoria have 
passed, for we may see them sporting about in the interior of the 
cell. 
Hedwig had noticed the beautiful structure of the Sphagnum 
leaf, for in his Pundamenta Hist. Nat. Muscorum,i.p. 25 (1782), he 
mentions the large areolz, void of chlorophyl, traversed by very 
fine vessels containing parenchyma, which he suggests may corre- 
spond to the ducts of flowering plants. 
Moldenhawer, however, detected the true nature of the areo- 
lation, and the two kinds of cells of which it is composed, with the 
presence of threads and pores in the vesicular cells, and Von 
Mohl still further extended his researches. 
The leaves of all Spagna consist of a single stratum of cells 
without any midrib, and these cells are of two distinct kinds 
alternating with each other: rst, narrow chlorophyllose cells 
(ductus intercellulares of C. Miiller, zxterstitia of Hampe), which 
form a frame or network of somewhat bent hexagonal meshes, 
and usually six of these cells enter more or less into forming the 
boundary of each mesh, their colour being green, yellow, or red, 
according to that of their contents ; these cells are really the most 
important part of the leaf, since they carry on the vital functions, 
and form the scaffold on which the hyaline cells are stretched : 
and, large colourless vesicular cells dropped as it were into each 
mesh of the network, and containing in nearly all species spiral 
fibrils on their internal wall and perforated with foramina; for 
