PRACTICAL^ERCISES ./ 31 



accordingly be more easily recognized. One or more 

 roundish, highly refractive bodies may be seen in the 

 nucleus (nucleoli). 



4. The cell-walls are not stained. 



a. Treat a fresh preparation with potash solution, 

 and warm gently over a spirit-lamp : observe that the 

 protoplasm, chlorophyll-grains> and nucleus lose their 

 definite outlines, and, undergoing a process of swelling, 

 become at the same time more transparent. This may 

 best be seen in a specimen which has been bleached in 

 alcohol. 



I. Mount another preparation in " eau de javelle " 

 (see Appendix A), and observe it at intervals for some 

 minutes : a similar result will be seen, viz. the contents 

 of the cells swell, and the whole tissue becomes more 

 transparent : this is especially the case in the region 

 near the apex of the prothallus. 



c. Irrigate a fresh specimen with a 2^ per cent. 

 solution of common salt, and watch the result : it will 

 be seen that the protoplasm contracts, often taking the 

 form of an almost spherical ball, thus separating from 

 the cell-walls with which it was originally in contact : 

 the latter will now appear as a continuous network of 

 partitions dividing the whole prothallus into a number 

 of chambers. 



If this preparation be examined under a high power, 

 a number of delicate protoplasmic filaments may be 

 seen connecting the outer surface of the contracted 

 protoplasm with the cell- wall : this indicates that the 

 two bodies are not merely in apposition in the living 

 cell, but are closely connected. 



A cell in this state is said to be plasmolytic : the 



