622 BOTANICAL TECHNIQUE 



Cellulose, as food reserve in seeds, etc., is preferably collected 

 before maturity. Cut sections under water rather than alcohol. 

 If dry and mature, treat like hard woods. 



Collenchyma and pectic substances are troublesome if too soft. 

 Preserve and cut in 70 per cent, alcohol, swelling with water 

 afterwards if required. A stronger alcohol may be used to harden 

 collenchyma if necessary, but subsequent swelling is more difficult. 



Crystals, as cell inclusions, show best in sections of fresh material 

 mounted in water or in 2 per cent, acetic acid. Mounted in balsam 

 they lose too much in visibility. 



Inulin. Cut material into small blocks and treat with several 

 changes of absolute alcohol to remove the water rapidly and 

 completely. Cut with a knife flooded with absolute alcohol. 

 Stain sections with a saturated solution of orange G in clove oil, 

 wash in xylol and mount ; inulin appears darker in colour than 

 the general tissues. 



Resin, e.g. in Gymnospermge, is preserved and stained by 

 immersion in saturated aqueous copper acetate solution for one 

 to several weeks ; wash the excess of copper acetate out and 

 preserve in 50 per cent, alcohol. The resin retains a bright green 

 colour when the sections are mounted in glycerin. 



Starch is better preserved in alcohol than in formalin or acidic 

 solutions which might hydrolyse it. Usually, however, it is 

 preferable to be rid of it. 



1237. Decalcification should be carried out as gently as possible. 

 Dilute hydrochloric acid (2 per cent.) is most generally useful ; 

 the concentration may be increased up to 10 per cent, for more 

 rapid results. Acetic acid is more gentle, nitric acid more violent. 

 If the material is soft, fix in formalin alcohol, harden, and decalcify 

 in strong alcohol by cautious addition of acetic acid. Formalin, 

 oxidising to formic acid, will reduce or remove lime from specimens, 

 especially if small in amount. Perenyi's solution is also sometimes 

 used. For more accurate preservation of calcified material fix 

 in chromo-acetic, sublimate acetic, Flemming, etc, and repeatedly 

 exhaust the material under a vacuum pump. 



1238. Desilification is usually carried out by means of hydro- 

 fluoric acid, either full or half-strength, in a wax or wax-coated 

 bottle. The chemically pure reagent should be used for more 

 delicate material, but the commercial preparation suffices for most 

 purposes. Dry woods should be boiled in water and exhausted of 

 air before treatment with HF. (See also §§ 1252 and 1253.) Whole 

 organs after fixation should be thoroughly freed of air by means 

 of a vacuum pump while soaking in strong alcohol. If parts of the 

 material are rather delicate, demineralisation is better carried out 

 in weak alcohol, than in water, to avoid maceration. 



Diaphanol (Leitz) is suitable for softening all indurated tissues 

 (lignified and chitinised, as well as silicified). 



