110 



Methods in Plant Histology 



and 91X58X15 mm. These are listed respectively at 50,60, and 

 80 Pfennige. As listed, these dishes are not glazed; care should 

 be taken to indicate that the dishes must be glazed inside (innen 

 glasirt). The tray, Petri dish, or whatever is used, should be slightly 

 smeared with glycerin, to prevent sticking. If several objects 

 are to be imbedded in one dish, it is best to have the dish as near the 

 temperature of melted paraffin as possible; otherwise the objects 



may stick to the bottom, 



and it will be impossible to 

 arrange them properly. Hot 

 needles are good for 

 arranging material. Great 

 care should be taken not to 

 have the dish too hot, since 

 too high a temperature not 

 only injures the material, 

 but also prevents a thorough 

 imbedding. Pour the par- 



imnnvn 

 HHWMII 



FIG. 20 



FIG. 21 



FIGS. 20, 21. Paraffin cakes of root-tips, the 

 upper (Fig. 20) showing a good arrangement, the 

 lower (Fig. 21) showing fewer tips and most of 

 these not in position to be blocked without injury. 



imbedding dish and 

 arrange them so as to facili- 

 tate the future cutting out 

 from the paraffin cake. 

 Look at Figs. 20 and 21, 

 representing the arrange- 

 ment of root-tips in a par- 

 affin cake. From a cake 

 like that in Fig. 20 it is 

 easy to cut out tips for sectioning. The arrangement, or rather the 

 lack of it, shown in Fig. 21, should be remembered only as an 

 exasperating example. 



After the objects have been arranged, cool the cake rapidly by 

 allowing the bottom of the dish to rest upon cold water. As soon as 

 a sufficiently firm film forms on the surface of the cake, let water 

 flow gently over the top. After the cake has been under water for a 

 minute, it may be placed under the cold-water tap to complete the 



