122 



BACTERIA IN RELATION TO PLANT DISEASES. 



few final touches on a good leather strop. The maintenance of good edges on 



microtome knives is a matter of great importance and considerable difficulty, and 



where much material is to be cut it is very economical of time to send away such 



knives to be put in order by some 

 expert. In recent years the writer 

 has sent all such knives to Charles 

 L/entz & Sons, Philadelphia, with 

 very satisfactory results. Knives 

 suitable for serial sections are shown 

 in fig. 1 14 A and C. In fig. 1146 is 

 shown one of a set of knives not in- 

 clined to spring and well adapted to 

 the cutting of hard material with a 

 long slant stroke. These knives were 

 made to order by L/entz & Sons at a 

 cost of about $6 each. An end-on 

 view of all these knives is shown in 

 fig. 1 14 a, &, c, d.. 



Many plant tissues, especially ma- 

 ture leaves, are full of very hard cal- 

 cium oxalate crystals, and the difficul- 

 ties of properly cutting such material 

 are very great. The cutting of thin 

 sections of bone would be quite as 

 easy. After even a few sections the 

 edge of the knife looks like a minia- 

 ture saw and the sections themselves 

 are badly torn, partly by the dulled 

 knife and partly by the movement of 

 p. |j2* the crystals themselves. In case of 



the yellow disease of the hyacinth the 



writer has never been able to make satisfactory thin sections, many of the soft cells 



being filled with bundles of very hard raphides which he has not been able to 



dissolve without serious injury to 



the tissues. In such cases thick 



free-hand sections are about all 



that can be hoped for. 



Serial sections are cut on the 



microtome. The one shown in 



pi. 13 and fig. 119 leaves nothing 



to be desired in the way of a 



perfect-working durable instrument. The ribbon-carrier is above the table at the left. 



The knife is stationary. The block moves up and down, and the razor-carrier 



*Fic. 112. A page from the paraffin record-book. The numbers on the slide-boxes (fig. 103) 

 correspond to numbers in this book. Two-thirds actual size. 



fFic. 113. A mounted slide of serial sections, showing manner of labeling. 



Fig. I13.f 



