346 SCIENCE PROGRESS. 



The cells of a particular region of the tissue are marked 

 by the finely granular character of their protoplasm, and 

 their freedom from starch or chlorophyll, though a certain 

 amount of tannin is present in them, and they are richer 

 in proteids than the other cells of the leaf. Using Millon's 

 reagent, which is a mixture of the two nitrates of mercury, 

 all the cells of the leaf blackened, but the colour was deepest 

 in those in question. On warming, the black tint gradually 

 disappeared, and was replaced by an orange-red in the cells 

 containing the enzyme, and by a faint pink in the ordinary 

 parenchyma. In an allied species, Cerasus hisitanica, which 

 contains tannin, but not enzyme, in the corresponding cells, 

 this orange-red coloration was not found to be developed 

 by the same treatment. The reaction was not therefore 

 due to the tannin, but to some peculiar proteid constituent 

 with which the enzyme is associated, or to the enzyme 

 itself, probably the former, as it resembles fairly closely the 

 ordinary proteid behaviour with Millon's reagent. By the 

 presence of this proteid body, and its response to the test, 

 the enzyme-containing cells could be recognised. Con- 

 firmatory tests for proteids bore out this opinion. CuS0 4 

 and KHO coloured these cells a violet-pink, while cells con- 

 taining only tannin did not react to it more than ordinary 

 parenchyma cells with their lining of protoplasm, which 

 stained a pale pink without admixture of violet. Similar 

 experiments led to the recognition of certain special cells 

 in various tissues of the horse-radish and other cruciferous 

 plants (10) which stood out in marked contrast from their 

 neighbours. They became orange-red, while the ordinary 

 parenchyma in which they were embedded only took on a 

 pale pink tinge. With Fehling's fluid these could also be 

 distinguished. The proteid contents could, with a little 

 care, be distinguished from the protoplasm of the cells in 

 which they were found. Treatment with alcohol of 50 per 

 cent, strength caused the whole contents to shrink a little 

 from the cell wall, and the proteid granules shrank from the 

 protoplasm itself, so that the contents and the protoplasm 

 could be seen separately. The latter was coloured orange- 

 red by subsequent treatment by Millon's reagent, while 



