294 
METHODS IN PLANT HISTOLOGY 
yourself master of Haidenhain’s iron-alum haematoxylin; then add 
the safranin, gentian-violet, orange combination; then safranin and 
anilin blue; and then experiment for yourself, but remember that the 
triumphs of modern cytology have been won with iron-haematoxylin 
and that you cannot read intelligently the literature of the past 
twenty-five years until you have gained at least an approximate 
mastery of this stain. Of course, dehydration, clearing, and infiltra¬ 
tion must be very gradual. The schedules by Yamanouchi and by 
Sharp, on pages 45 and 46, 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. 
If you use aqueous gentian-violet or crystal-violet, after the 
safranin is satisfactory, transfer to water and then to the violet. 
After staining in violet, dip in water to remove the excess of stain 
and then dehydrate rapidly in 95 per cent and absolute alcohol, 
differentiate in clove oil, and then transfer to xylol. 
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 5 mm. 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 2 mm. wide. Cut the latter longitudinally; the 
rectangular pieces are sufficient for transverse sections. Fix in 
chromo-acetic acid. The roots of Hordeum vulgare (barley) might 
also be suggested. 
The roots of Ranunculus repens and Sambucus nigra furnish 
good illustrations of the radial arrangement of xylem and phloem. 
