THE MACERATION METHOD. 159 



acid to completely cover them, 1 then lay on this fluid longitudinal 

 sections, not cu,t too thin, of the tissue to be investigated, and 

 warm it over a flame until active evolution of gas ensues. The 

 process should not be carried on in the same room with a 

 microscope, as the vapour evolved would injure it. We allow 

 the reagent to work for a few 7 minutes, till the sections appeal- 

 quite white, and then pour the whole into a large evaporating 

 dish, or saucer, full of water. The floating sections should be 

 removed from this, by means of a glass rod, into another vessel 

 filled with w^ater, so as to wash them ; and from thence into a 

 drop of water upon an object-slide. The preparation can here be 

 torn to pieces with needles, and the individual elements separated. 

 If the reagents have worked rightly, the pectose middle lamellae 

 between the elements will be dissolved, and their separation easy 

 to complete. All the elements which previously had been studied 

 in combination, will now be found isolated under the microscope. 

 They are usually well preserved, except that the lignin, by which 

 the cellulose in the wood had been chemically altered, having 

 been more or less completely removed, they for the most part 

 stain violet \vith chlorzinc iodine. 



Instead of chlorate of potash arid nitric acid, maceration can 

 be carried on by means of chromic acid. A concentrated aqueous 

 solution is used, and allowed to act for only a short time, perhaps 

 half a minute. Then wash with a large quantity of w r ater. The 

 sections must not be too thick, or they cannot be readily disin- 

 tegrated. In general this method is inferior to that of Schultze. 

 With herbaceous plants, when the middle lamellae between the 

 elements are not lignified, hydrochloric acid and alcohol can be 

 used for maceration ; a mixture of one part hydrochloric acid 

 and from five to three parts of alcohol. This fluid should act 

 upon the sections for about twenty-four hours ; then wash the 

 sections, treat them with an alkali, such as 10 per cent, solution 

 of ammonia, and the cells can be separated from one another by 

 slight pressure. 



In the case of Tilia we will preferably use Schultze's method, 



1 If the proportions of these reagents are not right, red fumes of nitrous 

 acid gas will be given off", and the tissue may be entirely dissolved. W. R. 

 McNab has suggested a fluid composed of two drachms nitric acid (of sp. gr. 

 1-10) and three grains of chlorate of potash, in which the tissue should 

 be kept for a fortnight, when the constituent elements can be separated 

 (Trans. Edin. Bot. Soc., xi., 293). 



