.30 PRACTICAL BOTANY 



arrangement of cells in two dimensions of space, i.e. 

 as a flat plate of tissue. Mount a small prothallus of a 

 Fern (or the thin lateral part of a large one) in water, 

 and examine it under a low power. 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 

 distinguish 



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 

 this observation. 



2. A colourless film of granular protoplasm (primor- 

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

 and surrounds 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 



