116 THE PLANT CELL. 



Higher Plants, the number of the primary chromosomes is 

 " reduced " to half of what it is during the vegetative division of 

 the same plant. This is known as cell-division with reduction. 



It occurs, for example, in Osmunda regalis in the mitoses occurring 

 in cells of the prothalkis (gametophyte). 



NoU. — Some of the various "fixing " reagents used for the preparation 

 of material for the study of mitosis, and also a list of plants and organs 

 suitable for this study, will be mentioned here. 



(a) Fleniming's Solution. — This is a very useful reagent for the rapid 

 fixation of quickly-growing tissues, such as root-tips, one modification of 

 it being as follows : — 



5 per cent, chromic acid, 10 c.c. 



2 per cent, osmic acid, 5 c.c 



Glacial acetic acid, 1 c.c. 



Distilled water up to 50 c.c. 



This solution may be used more dilute if required. Root-tips fix in it 

 in about 12 hours, and, after fixing, should be well washed in distilled 

 water and transferred progressively to the following strengths of alcohol : 

 — 50 per cent., 70 per cent., 90 per cent., and, finally, absolute alcohol. 

 By this method the tissue is hardened. For preserving after hardening, 

 the root-tips or other tissue should be kept in pure methylated spirit. 



(6) Chromic Acid. — This may be used in 5 per cent., or 2 per cent., 

 or j per cent, solutions in distilled water. It is not so good as Flemming's 

 solution as a fixing reagent. It may be made more useful by the addition 

 of acetic acid. 



(c) Absolute Alcohol. — This both fixes and hardens tissues, but is not 

 suitable for delicate organs. 



(d) A Mixture of Acetic Acid and Alcohol (about 55 per cent, strength) 

 is sometimes used as a fixing agent. 



(e) A Solution of Corrosive Sublimate in Alcohol (2 to 5 per cent.) is at 

 times a useful fixing reagent. It is used mostly for animal tissues, more 

 especially for the fixing and hardening of larval tissues. 



The most serviceable reagents for the fixation of plant-tissues, parti- 

 cularly for those in which it is desired to study mitosis, are Flemming's 

 solution and Chromic cu:id solution, since these, if xised dilute, will not 

 cause much preliminary shrinking of the cytoplasm. 



Plants suitable for the study of cell-division are the following : — 

 Hyacinthus (root-tips of water-cultures). Allium (root-tips of water- 

 cultures), Fritillaria (endosperm, root-tips of water-cultures), Lilium 

 maturation stages in the embryo-sac, pollen mother-cells), Larix (cortex 

 and medulla of young ? cone). 



Longitudinal and transverse sections should be made by cutting with a 

 flat razor in split pith, or tissues may be hardened and embedded in 

 celloidin or paraffin, and microtome sections made, a somewhat more 

 lengthy process. 



