8 CHLOROPHYLL. [CH. I 



phyll is soluble in these fluids. It is important to remem- 

 ber the difference between chlorophyll, a substance soluble 

 in alcohol, and a chlorophyll-body or chloroplast, which is a 

 special kind of protoplasm. In Spirogyra the chloroplasts 

 are of a remarkable spiral form, winding like corkscrews 

 round the cell, as shown in fig. 2. It is the spiral arrange- 

 ment which has given the name Spirogyra to the plant. 



In the cell-cavity is another organ, the nucleus, a part 

 of the protoplasm, denser and staining more easily than 

 the rest of the protoplasm, and having certain functions 

 which need not be discussed. It is suspended in the cell 

 cavity by ropes of ordinary protoplasm. The nucleus 

 contains one or more small bodies, the nucleoli. 



The treatment of Spirogyra with glycerine or strong 

 salt solution is recommended in the Practical Work 

 in order to illustrate an important fact, namely that the 

 cell is tensely filled with cell-sap, the protoplasmic lining 

 being blown out with cell-sap, as an air-cushion is blown out 

 with air. The glycerine or strong salt solution takes away 

 some of the water from the cell-sap and the protoplasmic 

 lining collapses. The importance of this observation will 

 appear later on, in a section devoted to the stability of 

 plant structures. 



Nutrition. 



Since the Spirogyra increases in substance in the water 

 in which it grows it is quite certain that this water must 

 contain the food materials which are transformed into new 

 protoplasm and new cell-walls. If the water be analysed 

 it will be found to contain in minute quantities lime, 



