20 PRACTICAL BOTANY 



It will be at once obvious that the thin plate of tissue, one 

 layer of cells in thickness, is partitioned off into a number of 

 cells of polygonal form, which are in close connection with one 

 another, so that no spaces intervene between them. Note the 

 green granules (chlorophyll-corpuscles or chloroplasts), which 

 are here to'be seen in considerable numbers in each cell. 



Examine the preparation under a high power, and dis- 

 tinguish 



1. The cell- walls, which are thin, highly refractive, and of 

 almost uniform width throughout : the extreme margin of the 

 prothallus will be found best adapted for their observation. 



2. A colourless film of granular protoplasm (primordial 

 utricle), which is in close apposition to the cell-wall, and sur- 

 rounds a large central cavity (the vacuole) full of colourless 

 cell-sap : in this protoplasmic film are embedded 



3. The chlorophyll-corpuscles or chloroplasts, which will 

 now be seen to be flattened disk-like bodies. 



4. A single, more highly refractive nucleus is to be found in 

 each cell, its position being variable. 



Treat the preparation with iodine solution, and observe 

 that 



1. The protoplasm will be stained brown. 



2. The chlorophyll-corpuscles, for the most part, a dusky 

 purple. 



3. The nucleus will be more deeply stained, and will ac- 

 cordingly -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, chloro- 

 phyll-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. 



b. Mount another preparation in " eau de javelle " (see Ap- 

 pendix 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 



