THE STRUCTURE OF THE CHARACE#, 351 
IIIT.—Ax1AL STRUCTURE. 
For a long time they were regarded as an undivided group, but 
a closer acquaintance has led to their being separated into several 
genera, of which the two princpal are Chara and Nitella. 
The first of these genera is easily recognized by the constitution 
of its stem ; there is a large central tube surrounded by a number 
of narrower tubes. The outer tubes do not enclose the inner tube 
in a perfectly straight direction, but most frequently exhibit a spiral 
torsion from one node to the next ; they are besides often encrusted 
with lime, which makes the plants very brittle to handle. 
The second of the two principal genera is named Nitella, and in 
this group the tubes are translucent, while the cortical series of 
smaller tubes is absent; this difference of structure makes the 
Nitellas more flexible and softer to handle than the Charas. 
The so-called stems of these plants are therefore composed of a 
single row of large axial cells or tubes placed end to end, and with 
or without cortical layer of narrower tubes. The extremities of the 
tubes are joined to their neighbours by a thin transverse plate 
made up of roundish cells, which constitute the node ; and, except- 
ing some hair-like processes, all the lateral out-growths originate 
from these nodes, giving rise to leaves or lateral branches in the 
upper portion, and to rhizoids or roots in their subterranean por- 
tion. The tubes are short at the growing end of the plant, but 
they increase in length considerably as they become distant from 
the terminal growing point. 
The subterranean portion is not unlike the aquatic portion, but 
it does not possess any cortical layer; a number of fine tubular 
radicles originate at the nodes serving to bind the plant to the 
mud. Sometimes the subterranean tubes inflate and produce 
small bulbs, bulbils, or tubercles, and even star-shaped bodies 
(Montagne, Annales, des. sc. nat. third ser. Vol. XVIII.), all of 
which are white in colour, and gorged with starchy matter which 
serves as a reserve of nutriment for the growing plant. 

IV.—STRUCTURE OF THE CELLS. 
All the young cells or tubes possess a nucleus, which at the 
outset is found in the centre of the protoplasmic mass. The cells 
increase by division, but each act of sub-division is preceded by 
the dissolution of the primitive nucleus and the formation of two 
new nuclei; further changes follow in the protoplasm which now 
lines the inner walls with a thick deposit. 
From this time commences a rotatory movement in the cell 
contents, always in the direction of the long diameter. This 
peculiar movement is not confined to the tubes of the stem, but is 
met with in every cell of the plant; it is, however, best observed 
in the large translucent tubes of the Nitelle. It is very difficult to 
