XL] SPIROGYRA. 403 



Spirogyra will not of course grow in distilled water any 

 more than will Yeast or Protococcus. If the water be sup- 

 plied with the following salts the Spirogyra will b able to 

 obtain all the food it requires : Potassium Nitrate, Calcium 

 Sulphate, Magnesium Sulphate, Calcium Phosphate, Sodium 

 Chloride, and Ferric Chloride. The sodium chloride is only 

 of indirect service as neither of its elements is essential as a 

 food-constituent. As regards the other elements required 

 by the plant, we already know that Carbon, Hydrogen, 

 and Oxygen are the elements of starch and cellulose, while 

 the protoplasm and nucleus are built up of these elements 

 with the addition of Nitrogen, Sulphur and Phosphorus. 

 Iron is necessary for the formation of chlorophyll, while 

 potassium plays an essential, though obscure, part in the 

 process of assimilation. Calcium and Magnesium have 

 been shown by experiment to be necessary for the nutrition 

 of green plants, but their exact function is still doubtful. 



LABORATORY WORK. 



A. MORPHOLOGY. 



I. Vegetative condition. 



1. Naked-eye characters. 



Observe that the masses of Spirogyra consist of 

 long, delicate, bright green, unbranched filaments, 

 which in the vegetative condition are quite smooth 

 and glossy. 



2. Microscopical characters. 



Mount one or two filaments of Spirogyra in water 

 and observe first with the low, and then with the 

 high power. 



262 



