256 



METHODS IN PLANT HISTOLOGY 



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mycelium for several days and then transferring it to pure water or to 

 distilled water. As long as the nutrient solution is sufficiently strong 

 and fresh, only sterile mycelium will be produced. 



To secure oosporic material, mycelium which has been highly nour- 

 ished for several days in a nutrient solution is brought into a 0.1 per 

 cent solution of leucin, or into a 0.05-0.1 per cent solution of haemo- 

 globin. Begin to examine after 24 hours, 



Oogonia have been produced in great numbers by the following 

 method: cut ordinary corn {Zea mais) into small pieces and boil for 20 



minutes. When cool, put 

 pieces into a Petri dish and 

 add enough pond water to 

 nearly cover the pieces of 

 corn. Oogonia may appear 

 within 3 or 4 days. 



For fixing, the following 

 formula is excellent for 

 material which is to be 

 mounted whole: 



Formalin 10 c.c. 



Glacial acetic acid. . . 5 c.c. 

 Water 85 c.c. 



Fix at least 24 hours, 

 but material may be left 

 for months in this fixing 

 agent. 



Stain some in phloxine 

 and anilin blue, and some 

 in iron-alum haematoxylin. 

 Mount some of each lot on 

 each slide (Fig. 65). 



For sections, it is bet- 

 ter to fix in the Chicago 

 chromo-acetic-osmic acid 



Fig. 65. — Saprolegnia: A, a fly with three days' growth 

 of Saprolegnia, natural size. B, two sporangia, the one on 

 the left with nearly mature zoospores and the one on the 

 right with mature zoospores escaping. Can oogonium with 

 9 eggs; 5 antheridia are shown. B, C, and D X300. From 

 Chamberlain's Elements of Plant Science (McGraw-Hill 

 Book Co., New York). 



solution. 



Satisfactory material for general laboratory purposes can be secured 

 as just described. Absolutely pure cultures can be secured only by ob- 

 serving all the precautions necessary in bacteriological work. 



Achlya is sunilar and equally good for illustrative purposes. It is 



