70 ON THE STRUCTURE OF THE ROOT. 



important that the razor should be kept quite level and the piece 

 of root in an upright position, otherwise there would be a danger 

 of the sections being cut obliquely. 



If any difficulty be found in holding the root firmly, it should 

 be embedded in pith in the following manner : — Take a piece of 

 elder pith, about one-third of an inch in diameter and as long as 

 the material to be cut. Slice away the outer hard portions, and 

 divide the remaining soft cylinder longitudinally in half. On the 

 inner flat face of each half make a groove sufticiently deep and 

 parallel to the sides, and fit the piece of root into these grooves ; 

 fasten the halves together with a ribbon pin and place the whole 

 into 70 per cent, alcohol for a minute. The root is now supported 

 on all sides by the pith, and sections are cut through pith and all. 

 These are transferred to a watch-glass of 70 per cent, alcohol, and 

 the pith sections picked out with a camel-hair brush. Draw off 

 the alcohol by means of a pipette with an aperture too small to 

 allow the sections to pass in, and add 30 per cent, alcohol. After 

 the sections have come to rest, remove the weak alcohol and add 

 water. 



2. — Staining. Replace the water with a solution of iodine 

 green and allow to stand for an hour, when the sections will be 

 found to be much overstained. Draw off the iodine green and 

 rapidly wash in 50 per cent, alcohol, which should be then drawn 

 off quickly. Now treat the sections with a solution of Bismarck 

 brown for ten minutes, and wash rapidly in 70 per cent, alcohol. 



3. — Dehydration. The sections are now placed in methylated 

 alcohol and then into absolute alcohol, to free them from all trace 

 of water. 



4. — Clearing. Replace the alcohol with a mixture of equal 

 parts of absolute alcohol and oil of cloves. When the sections 

 have come to rest, remove the mixture and add oil of cloves. 



5. — Mounting. — The sections may now be picked out with a 

 dry camel-hair brush and mounted in balsam. The section should 

 be placed on the middle of the slide, a single drop of balsam 

 placed on it, and covered by a thin, clean cover-glass. The pre- 

 paration may be examined at once, but will not be dry for some 

 days. 



By this method the xylem, endodermis (and suberised tissue 



