ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
715 
and partly from their chemical composition. Another prominent phy- 
sical source of purification is the deposit of floating particles, all of 
which, on account of their density, tend to fall to the bottom. These 
not only subside, but in the course of their precipitation drag other 
bodies with them. This action is aided by the molecular adhesion of 
water and the particles, and from this several methods have been devised 
for the artificial purification of water, such as Clark’s and Anderson’s, 
in which chalk and sesquioxide of iron are used. But the purification 
of water is effected more surely when an organic or mineral precipitate 
is formed than when the microbes are left simply to the action of gravity 
or of molecular adhesion. The principal agent in the purification is, 
however, the microbe, which restores to the inorganic world the elements 
of living matter ; the part played by organisms is the principal one, the 
role of the physical actions is subsidiary. 
B. CRYPTOGrAMIA. 
Cryptogamia Vascularia. 
Vegetative Organs of Vascular Cryptogams.* — M. G. Poirault 
enters into various details respecting the structure of the root, stem, and 
leaf of Filices, Marattiaceae, and Ophioglossacese. 
With regard to the root, several species of Oleandra present struc- 
tures resembling the rhizophores of the Selaginellaceae. With the excep- 
tion of Botrychium and the Ophioglossacese, all Vascular Cryptogams 
belonging to these classes have root-hairs. While aerial roots possess 
a cuticle, those growing in the soil have it replaced by a mucilaginous 
layer. Ceratopteris thcilictroides has roots which penetrate the cortex. 
The cell-walls of tbe roots of many ferns possess wart-like protu- 
berances. Those of the endoderm are characterized by remarkable 
projections. The pericycle is always composed of parenchymatous 
elements. The phloem-fibres of the vascular bundles consist of phloem- 
cells and sieve-tubes ; the former are elongated, and contain a large 
nucleus and abundant protoplasm. In the xylem the vessels are usually 
arranged in a band, of which the two extremities constitute the proto- 
xylem, and the central portion the deuteroxylem. There may or may 
not be a metaxylem ; it is wanting in the roots of the Marattiaceae and 
Ophioglossacese. The root-buds are described in detail, especially in 
the Ophioglossacese. They are of endogenous origin. 
In the stem, the sclerotized cells in the cortex are very remarkable. 
In the leaves strands of protoplasm connecting the cells occur very 
commonly, not only between the elements of the same, but even between 
those of different tissues. Crystalloids occur in a very large number of 
species, especially in the Polypodiaceae and Cyatlieaceae. Crystals of 
calcium oxalate are also widely diffused. 
Muscineae. 
Respiration and Assimilation in Muscineae. f — M. B. Jonsson has 
studied twenty-five species of mosses, Sphagnums, and Hepaticae, and 
* Ann. Sci. Nat. (Bot.), xviii. (1894) pp. 113-256 M3 figs A 
t Comptes Rendus, cxix. (1894) pp. 440-3. 
