678 ANNALS OF THE MISSOURI BOTANICAL GARDEN 



[Vol. 2 



and a piece about 2 mm. square on the hymenial surface is cut 

 out with a scalpel. If material is abundant the process may be 

 reversed and a larger piece than needed may be cut out with 

 the scalpel, trimmed to the requisite size, immersed in 95 per 

 cent alcohol for a few seconds and then transferred to water. 

 In the writer's experience the latter method is the more pref- 

 erable and has probably been the one most used. The ma- 



- 



terial does not soften while in alcohol, but that reagent is 

 used only to facilitate the absorption of water by the tissue. 

 Any rigidity that may be imparted to the tissue by the alcohol 

 is probably overcome when the material is transferred to 

 water. In some cases when this transfer is made the tissue 

 either becomes very soft or very friable so that no razor, how- 

 ever keen, will cut a clean section through it. It is here that 

 the latter method obtains preference over the former, for 

 after some experience one can judge of the probable effect the 

 water will have and by shortening the period that the material 

 remains in the water the tissue is in better condition for sec- 

 tioning. 



The most instructive preparations are often those contain- 

 ing both longitudinal and cross-sections of the tubes. Such 

 sections are easily obtained in one mount by cutting out the 

 piece of material somewhat longer in one direction than stated 

 above — say about 2x4 mm. on the surface. Several longi- 

 tudinal sections may be cut from this and the position of the 

 remaining bit of tissue so changed that cross-sections may be 

 obtained. 



For sectioning, the tissue is placed in the proper position 

 in a piece of pith and as the sections are cut they may either 

 be transferred directly to the slide by means of a camel 's- 

 hair brush dipped in alcohol, or they may be allowed to ac- 

 cumulate in the alcohol on the razor and then flooded off into 

 a watch-glass containing alcohol. By the last method one can 

 pick out with more accuracy the thinner sections by observing 

 them under the lens of a low-power dissecting microscope. 

 The writer has found it to be sufficient in most cases to trans- 

 fer the sections directly to the slide, disregarding the thicker 

 sections that are cut, or brushing them off the edge of the 



