260 



THE MICEOSCOPE AND ITS REVELATIONS. 



formed as in Batrachospermeae, save that the investing cells grow up- 

 wards as well as downwards from each node, and meet each other on the 

 stem half-way between the nodes. 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.' The long tubiform cells of Nitella afford a very beautiful 

 and instructive display of the phenomenon of cyclosis, or rotation of fluid 

 in their interior. Each cell, in the healthy state, is lined by a layer of 

 green oval granules, which cover every part, except two longitudinal lines 

 that remain nearly colorless (Fig. 153, B); and a constant stream of semi- 

 fluid matter containing numerous jelly-like globules is seen to flow over 



"El 153. 



Nitella flexilis: A, stem and branches of the natural size; a, 6, c, d, four verticils of branches 

 issuing from the stem ; e, f, subdivision o t f the branches ; B, portion of the stem and branches en- 

 larged; a, 6, joints of stem; c, d, verticils'; e,f, new cells sprouting from the sides of the branches; 

 g, n, new cells sprouting at the extremities of the branches. 



the green layer, the current passing up one side, changing its direction 

 at the extremity, and flowing down the other side, the ascending and de- 

 scending spaces being bounded by the transparent lines just mentioned. 

 That the currents are in some way directed by the layer of granules, ap- 

 pears from the fact noticed by Mr. Varley, 1 that if accident damages or 

 removes them near the boundary between the ascending and descending 

 currents, a portion of the fluid of the two currents will intermingle by 

 passing the boundary; whilst, if the injury be repaired by the develop- 

 ment of new granules on the part from which they had been detached, 

 the circulation resumes its regularity, no part of either current passing 

 the boundary. In the young cells, however, the rotation may be seen 



1 "Transactions of the Microscopical Society," 3d Series, Vol. ii., p. 99. 



