152 Plant Tissue Culture 



or hole. A clean cover is grasped between the 

 thumb and middle finger of the left hand (the form 

 of the rack used facilitates this) and, while it is 

 held horizontal, a drop of nutrient solution is 

 placed on the middle of the cover. This is spread 

 around in a uniform thin layer about 8 mm. in 

 diameter. The fragment of tissue is then placed 

 in the center of the drop, the cover is inverted 

 with a quick, smooth motion so as not to throw off 

 the drop of liquid, and is pressed down over the 

 depression of a slide. The slide is set to the 

 operator's right and the process repeated. After 

 a sufficient series is completed, the covers are 

 ringed with hot paraffin or vaseline, using a small 

 brush, so as to seal them. They are then ready for 

 observation or incubation. 



Hanging-drop cultures should be transferred to 

 fresh nutrient at least every 3rd or 4th day. If 

 regular depression slides are used, this will neces- 

 sitate removing the cover carrying the culture, a 

 process which requires great care (Parker, 1938, 

 26). If special pierced slides are used, it is only 

 necessary to slip out the lower cover, draw off the 

 nutrient with a clean pipette, replace it with a 

 fresh drop, and insert a clean cover in place of 

 the one removed. 



