164 Methods in Plant Histology 



A stock solution which can be diluted as required may be made as 

 follows : 



Potassium nitrate, KNOs 1 g. 



Magnesium sulphate, MgSCX 1 g. 



Calcium nitrate, Ca(N0 3 )2 3 g. 



Potassium phosphate, K 2 HP04 1 g. 



Dissolve the first, second, and fourth ingredients in 1 liter of 

 distilled water, and then add the calcium nitrate. A precipitate of 

 calcium phosphate will be formed. For practical purposes this may 

 be called a 0.6 per cent solution. Whenever a dilute solution is 

 made from the stock solution the bottle must be shaken thoroughly 

 in order that a proper amount of the precipitate may be included in 

 the diluted solution. To make a 0. 1 per cent solution, add 5 liters of 

 distilled water to 1 liter of the stock solution; for a 0. 3 per cent solu- 

 tion, add 1 liter of distilled water to 1 liter of the stock solution, etc. 



The addition of a liter of a . 2 per cent solution to 4 or 5 liters 

 of water will often produce a more thrifty growth. Directions for 

 inducing reproductive phases are given in connection with the various 

 types. With a good supply of glass jars, plenty of Knop's solution, 

 a reasonable control over temperature, and the teacher's usual 

 amount of patience, most laboratory types can be studied in the 

 living condition at all seasons of the year. 



Permanent preparations are needed to show details which are 

 not so evident in the fresh material. The unicellular and filamentous 

 members, together with such forms as Volvox, are best prepared by 

 the Venetian turpentine method. The structure is so much more 

 complicated than in the Cyanophyceae that it demands far more 

 care and skill to make good preparations. In some of the green 

 algae, like Spirogyra and Closterium, it has been found that cell 

 division takes place most abundantly in the night; mitotic figures 

 are scarce in material collected in the daytime. From an hour before 

 midnight up to three or four o'clock in the morning is the best time, 

 if you want dividing stages. Chromo-acetic acid is a good killing 

 and fixing agent for the whole group. Very good results have been 

 obtained by adding about 3 c.c. of 1 per cent osmic acid to 100 c.c. 

 of chromo-acetic acid (Schaffner's formula). If material is to be 



