KOTATION IN CELLS OF CHAR A, 



323 



the purposes of observation, in large glass jars exposed to the 

 light; all that is necessary being to pour off the water occasion- 

 ally from the upper part of the vessel (thus carrying away a film 

 that is apt to form on its surface), and to replace this by fresh 

 water. Each plant is composed of an assemblage of long tubi- 

 form cells, placed end to end; with a distinct central axis, around 

 which the branches are disposed at intervals with great regular- 

 ity (Fig. Ill, a). In one of the genera, Nitella, the stem and 



FlQ. 111. 



NiteUa fiexUis : — A, stem and branches of the natural size; a, 6, c, d, four verticils of branches 

 issuing from the stem ; e, /, subdivision of the branches ;— b, portion of the stem and branches en- 

 larged; a, &, joints of stem ; c, d, verticils ; e, /, new cells sprouting from the sides of the branches ; 

 ^, h, new cells sprouting at the extremities of the branches. 



branches are simple cells, which sometimes attain the length of 

 several inches; whilst in the true Ohara, each central tube is 

 surrounded by an envelope of smaller ones, which is formed as 

 in Batrachospermese, save that the investing cells grow upwards 

 as well as downwards from each joint, and meet each other on 

 the stem half-way between the joints. Some species have the 

 power of secreting carbonate of lime from the water in which 

 they grow, if' this be at all impregnated with calcareous matter; 

 and by the deposition of it beneath their teguments, they have 

 gained their popular name of " stone-worts." These humble 

 plants have attracted much attention, in consequence of the 

 facility with which the "rotation," or movement of fluid in the 

 interior of the individual cells, may be seen in them. Each cell, 



