File:Text-book of structural and physiological botany (1877) (14589565920).jpg

Identifier: textbookofstruct00thom (find matches)
Title: Text-book of structural and physiological botany
Year: 1877 (1870s)
Authors: Thomé, Otto Wilhelm, 1840- Bennett, Alfred William, 1833-1902
Subjects: Plant physiology
Publisher: New York : J. Wiley & sons
Contributing Library: Smithsonian Libraries
Digitizing Sponsor: Biodiversity Heritage Library

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direction of the currents of proto-plasm, (x 800.) Kerria japonic a. A violet colour is always, a blue colour usually, dueto dissolved pigments. As an example how peculiarly the separatepigments may be distributed in different superimposed layers of cells,the marginal flowers in the capitulum of Zinnia elegans are scarlet on theupper, light yellow on the underside, the uppermost layers of cells con-tain a purple sap with orange granules, all the rest a colourless sapwith a smaller number of light yellow granules. Only those cells whichare filled with air appear white ; a black appearance depends on a darkshade of a violet or brown colour. The conditions which favour theformation of the bright pigments are not yet known ; the agency of 26 Strtictural and Physiological Botany. light is not probable, since the bright colouring of flowers appears assoon as the form of the parts of the flower is determined, even thoughin the dark. Still more widely distributed in the vegetable kingdom than
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chlorophyll is starchy formed and found likewise only in those cells whichare invested with a cell-wall. With a great external variability, grainsof starch possess the common characteristic of turning an indigo-blue The Cell as an Individual. 27 colour on treating with an aqueous solution of iodine. * They have thesame chemical composition as cellulose, CgHioOg ; they are insoluble incold water, but swell up very strongly in boiling water, forming apaste. If starch mixed with saliva is heated for some time to 45° or55^ C, the substance which is coloured blue by iodine is removed. Theconclusion which naturally follows, that starch consists of the substancethat is coloured blue by iodine, granuloses together with a cellulosesubstance that is not so coloured, 0,2^^^. farinose^ must not, however, beconsidered as finally determined. The grains of starch are always

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