852 SUMMARY OF CURUENT RESEARCHES RELATING TO 



Tho spirit-lamp is a metal box filled with tow, and covered with wiro 

 gauze. 



Preservation of Plants in Spirit and the Prevention of Browning.* 

 — Dr. H. do Vrics describes tho following methods for iirescrving 

 vegetable tissues in spirit and for the prevention of browning. 



As the cause of the browning must bo sought in certain uncoloured 

 matters present in tlio cell-juices, and which by oxidation become 

 brown, it follows that the first object is to remove these substances from 

 tho jireparations before they become oxidized. It has long been known 

 that many leaves become less darkly coloured, if, before tlie death of tho 

 cell, the air be removed (by means of the air-pump or boiling). 



Boiling in water and then placing the jircparation afterwards in cold 

 spirit frequently gives satisfactory results, e. g. in Viscus alhis. An 

 excellent method is to boil the parts of the plants in spirit. Loaves of 

 rhododendron, Viscus, Aucuba, which are only immersed for five minutes 

 in boiling spirit, become quite decolorized afterwards, a result which, at 

 any rate in Aucuha, can bo attained in no other way. 



Another method which, with the exception of Aucuha, gave excellent 

 results, is to kill the plants in spirit to which abont 2 per cent, hydro- 

 chloric, sulphuric, or acetic acid has been added. Tho preparations arc 

 kept in this fluid for several months and then transferred to spirit 

 without acid. This is removi d from time to time until all the colouring 

 matter has been removed. The long stay in the acid fluid does not at 

 all injure the plants as they are just as useful for microscopical purposes 

 as fresh or otherwise preserved organs. Even the cr^-stals of oxalate of 

 lime are not dissolved by the mixture of spirit and hydrochloric acid, 

 although they are when the acid is mixed with water. In this way 

 completely decolorized preparations of Monotrojm and OrohancJie can be 

 obtained, and this fluid will also prevent Boletus from becoming blue. 



As the oxidation products are partly insoluble in acid alcohol, organs 

 do not become thoroughly decolorized by the fluid ; thus the bracts of 

 Plantago lanceolaia retain their colour, and in unripe fruits the places 

 where the flowering parts were attached can still be recognized, because 

 these parts were dead before they came into the acid si)irit. 



The decoloration of preparations which have already become brown 

 can only be effected by oxidation. The most effective reagents for 

 this purpose are chlorate of potash or soda vvith sulphuric acid. This 

 completely or almost completely removes the browning. The prepara- 

 tions are placed in spirit to which ' 2-0 • 5 ccm, per cent, of strong sul- 

 phuric acid and a small quantity of chlorate of potash crystals are added. 

 If the vessel be shaken from time to time, oxidation will bo completed 

 in 6 to 8 days ; any trace of pigment left after this time will always be 

 unaffected by the solution. The preparations are then transferred to 

 spirit. 



Another method of preservation consists in the use of a one per cent, 

 solution of picric acid. The prei^arations, however, become stained 

 yellow and always remain flabby, but as the chlorophyll is unaltered by 

 the solution, it is very useful for preserving variegated flowers. Spirit 

 through which sulphurous acid has been passed until a largo quantity 

 has been taken up gives satisfactory results. Pure glycerin is not 



* Maandblud van N.ituurwetenscliappen, IfSC, Nus. 1, 5, and 6, 1887, No. 4. 

 Ilandelingen van het eerste Natuur- en Genecskundig Congres te Amsterdam, 1887, 

 p. 139. See this Journal, 1887, p. 675 ; 1886, p. 107.5. 



