PRACTICAL EXERCISES 2? 



d. Treat a fresh preparation of the Apple pulp with 

 chlor-zinc-iodine (Schulze's solution), and examine it 

 under a high power : observe 



i. That the protoplasm is stained brown as with 



the iodine solution above used, 

 ii. That the cell-wall is stained violet. 



It is to be noted that the stain does not always 

 succeed at once, but time should be allowed for the 

 colour to develop : also that the colouring is not always 

 uniform, so that though the presence of the colour is 

 characteristic of cellulose, its absence does not 

 prove that there is no cellulose present: this reaction 

 affords good positive, but not trustworthy negative, 

 evidence. 



II. The simple specimen above described, though 

 derived from the complicated mass of tissue of which the 

 Apple consists, will serve to illustrate the appearance of 

 single cells, since these are readily isolated by the 

 process of teasing : the next specimen to be studied 

 will illustrate the aggregation of cells in a linear series, 

 so as to constitute a simple filament. 



Mount a small quantity of the fresh, filamentous Alga 

 Spirogyra in water (this Alga is commonly to be found 

 in summer in stagnant, or slowly flowing, fresh water, 

 as bright green flocculent masses, which are slimy to 

 the touch) : examine it first under a low power, and 

 observe on one of the largest specimens 



1. That the cylindrical filament is limited by a 

 definite cell-wall. 



2. That transverse partitions septa which are con- 

 tinuous with the limiting cell-wall, divide the filament 

 into a linear series of cells. 



