46 JOURNAL OF THE ROYAL HORTICULTURAL SOCIETY. 



parenchyma. Sometimes a non-diseased portion of tissue with a 

 number of bundles will show a coloration as intense as that appearing 

 in a diseased slice. Again, the bundles occurring in the diseased areas 

 are generally of a yellowish or dark colour before applying the test, so 

 that the coloration is more intense than it should be if due to the 

 reagent alone. These points have been taken into consideration in 

 estimating a difference in the intensity of coloration between the 

 members of parallel series. 



Brandt's Reactio-n. — This reagent was prepared by dissolving "3 gm. 

 of sodium selenate in a mixture of 8 c.cm. of water and 6 c.cm. of con- 

 centrated sulphuric acid. Parallel series of potato slices were cut as in 

 the above-mentioned experiments and placed in test tubes containing 

 the reagent. The preparation was then gently warmed until the first 

 appearance of colour in the slices. The colour changes take place much 

 more quickly than those brought about by the use of Mandelin's re- 

 agent. Various shades of red appear — raspberry-red and then currant- 

 red — this colour passes into a brownish yellow and finally all colour 

 disappears. . G. Meyer and von Klepzow found ten times as much 

 in the young sprouts as in the starch-parenchyma. Jorissen and Gros- 

 jean"^ also found a relatively greater quantity in the fresh early shoot. 

 In order to test the efficacy of the qualitative test, comparative slices 

 were made from the pith and young sprouts of the variety * Duke of 

 York. ' A much more intense coloration was obtained in the slices from 

 the sprout. Comparative slices from the starch-parenchyma and sub- 

 cuticular tissue of ' President ' were tried, but the test was inconclusive. 

 In the case of ' Factor, ' the sub-cuticular tissue yielded a slightly 

 stronger reaction than the starch-parenchyma. The difference in the 

 amount of solanin obtained by G. Meyer and von Klepzow from the 

 sub-cuticular tissue and the starch-parenchyma, however, was only 

 0.05 gms. in 1000 of material. The fact that the quahtative tests do 

 actually express a difference already known to exist from the results 

 of quantitative analysis lessens one's reluctance to accept the results 

 obtained from tests of this kind. Using parallel series of diseased and 

 non-diseased slices obtained from similarly situated tissue of the same 

 potato, a stronger coloration was again obtained in the diseased ones. 

 This reaction has advantages over Mandelin's, notably in that, owing to 

 warming the slice, there is less trouble from occluded bubbles, and that 

 the reaction takes place more rapidly. In this case also the vascular 

 bundles of the slices were relatively strongly coloured, and the cylinder 

 of bundles in those obtained from the young sprouts of the * Duke of 

 York ' variety was particularly conspicuous. 



Discussion of Probable Cause of Bruise. 

 It has been shown in a particular case that tubers affected with 

 bruise, when transferred to conditions of soil and climate other than 

 those under which they were raised, produced healthy ones. It has 



* Jorissen u. Grosjeax. Bidl. Acad. roy. hclg. (5), torn. xix. (1890), 

 p. 245. 



