OSCILLARIA GLfEOCAPSA. 263 



with 1 per cent, chromic acid or concentrated picric acid, and 

 stained with logwood. It matters little what species is used 

 for examination, but preference should be given to the thicker 

 forms, with more distinct partition walls, as represented in 

 Fig. 100. 



Movements of Oscillaria. The phenomena of movement, as we 

 must have noticed from the very beginning of our observation of 

 the Oscillariae, are very interesting ; and with a sufficiently strong 

 power we shall be able to study the phenomena best in the thicker 

 forms, with bent end and distinct granules. We then determine 

 that with the movement of the thread is combined a slow rotation 

 on its axis. Simultaneously the thread shows irregular flexions, or 

 nutations, which are the expression of differences in the rate 

 of growth on its different sides. These flexions usually take place 

 slowly ; but violent movements can be induced when the flexion 

 is stopped by some obstacle, and, by overcoming this, the tension 

 is suddenly relieved. The Oscillaria-threads move now forwards, 

 now backwards. The movements can only take place when the 

 threads are in contact with some other object. The straight 

 threads move like those which are bent ; in these latter the 

 phenomenon is, however, especially striking, and at once visible, 

 while in the straight threads it is necessary to fix the attention 

 upon individual granules, in order to demonstrate a rotation of the 

 thread on its axis. 



Structure of Glceocapsa. To the same class of organisms as 

 the Nostocaceae and the Oscillariae belong the still more simply 

 constructed Chroococcaceae, which we will study upon one of the 

 widely-distributed species of Glceocapsa. We choose G. polyder- 

 matica^ (Fig. 101), growing upon damp walls or rocks, recognisable 

 as a dirty-green to olive-green gelatinous layer. Under the 

 microscope we find a gelatinous envelope divided by delicate 

 walls, showing lamination ; and within it uniformly-coloured cells, 

 more or less clearly granular, and devoid of nucleus. By these 

 peculiarities of their cell-body the Chroococcacese are distinguished 

 from Protococcaceae and especially Palmellaceae, which in many 

 forms very strongly resemble them, but which have a nucleus, 

 and chromatophores, separated from the rest of the protoplasmic 

 body. 



1 More readily obtainable, and very similar, is G. caldariorum, a species 

 growing commonly on the walls, flower-pots and glass, etc., in conservatories 

 and greenhouses. [Eo.] 



