264 Methods in Plant Histology 



decades until you have gained at least an approximate mastery 

 of this stain. Of course, dehydration, clearing, and infiltration must 

 be very gradual. The schedules by Yamanouchi and by Sharp, on 

 pp. 42 and 43, will repay careful study. 



In staining with safranin, gentian- violet, orange, allow the 

 alcoholic safranin to act for 16 to 24 hours; then extract it with 50 

 per cent alcohol, slightly acidulated with hydrochloric acid, if neces- 

 sary, until the stain has almost disappeared from the spindle; then 

 pass through 70, 85, 95, and 100 per cent alcohol; stain in gentian- 

 violet dissolved in clove oil, or in a mixture of clove oil and absolute 

 alcohol, for 5 to 20 minutes; follow with orange dissolved in clove 

 oil, remembering that this will weaken the safranin and sometimes 

 the gentian-violet; finally use pure clove oil to differentiate the 

 gentian-violet. Leave the slide in xylol for 2 to 5 minutes to remove 

 the clove oil and to hasten the hardening of the balsam. 



The structure and development of the young root will be shown, 

 to some extent, in preparations made for mitotic figures. The origin 

 of dermatogen, periblem, plerome, and also of protoxylem, is well 

 shown in Zea Mays. An ear of sweet corn, as young and tender as 

 you can find on the market, will furnish material. Cut out from the 

 grain a rectangular piece about 2X3 mm. and 4 or 5mm. long; if 

 you want to show also the structure of the entire grain, take a section 

 the entire length of the grain, perpendicular to the flat side of the 

 grain, and about 2mm. wide. Cut the latter longitudinally; the 

 rectangular pieces are sufficient for transverse sections. Fix in 

 chromo-acetic acid. 



The roots of Ranunculus repens furnish good illustrations of the 

 radial arrangement of xylem and phloem. Smilax shows the radial 

 arrangement, with a large number of poles and a very highly differ- 

 entiated endoclermis. The origin of secondary xylem and phloem is 

 well shown in Sambucus nigra. Vicia Faba shows very clearly the 

 origin of secondary roots. The arrangement of cells in the young- 

 roots of aquatic or semi-aquatic plants is often extremely regular 

 (Fig. 93). 



The Leaf.- -Young and tender leaves should be fixed in formalin 

 alcohol and cut in paraffin. Cut sections freehand whenever there 



