62 DIFFERENTIATION AND SPECIFICITY OF STARCHES. 



considerable size. In the cells they sometimes constitute the only non-nitrogenous nutrient 

 reser\'e substance; sometimes other equally important compounds, such as fat, cellulose, 

 pectin bodies, etc., are present. In most cases the grains lie immediately within the cell- 

 cavity, and when present in large numbers they fill up the whole sj^ace and are sometimes 

 so crowded that they become flattened by mutual pressure into polyhedrous forms. They 

 may be in direct contact with each other, or a thin layer of protoplasm may intervene, so 

 that each grain appears to be lodged in its own compartment. When they are present 

 in smaller masses they frequently form a lining to the wall of the cell, and may if they 

 lie in a single layer become polygonal, owing to their crowded position; if still less numerous 

 they sometimes cover merely the cell nucleus or circumscribed places of the cell. 



The starch-grains during their entire existence, or at least in earUer stages, are inclosed 

 within plastids. In the nuclei and in the mucilage cells there may also occur oil-drops, 

 mucus granules, and chlorophyl granules. Starch usually occurs alone in the chlorophyl 

 bodies, but occasionally oil-drops are present. Owing to the crowded position of the 

 grains they are sometimes flattened by mutual pressure and may remain coalesced as a 

 pseudo-compound grain if set free by the disappearance of the surrounding protoplasm. 



In the clilorophyl of the Desmidacece and the Zygnemacecc, as well as in several other 

 lower forms of Algce, the starch appears first in the form of homogeneous rings (globular 

 shells) inclosed in protoplasm, and which later, through radial division, are converted into 

 a compound, spherical, hollow grain. 



PECULIAR KINDS OF STARCH, AND STARCH-LIKE BODIES. 



A substance termed soluble starch was found by Dufoiu- (Bull, de la Soc. vaud. de Sci. 

 nat., XXI, Nr. 93; Zimmermann, Botanical Microtechnique, 1893, 229) in solution in the 

 cell-sap of the epidermal cells of a few plants, notably Saponaria officinalis. The chemical 

 composition was not determined, but it agrees with the soluble starch made in vitro from 

 starch-grains in forming a solution in water, and in yielding a blue, violet, or red reaction 

 with iodine. Ewart (Pfeffer's Physiology of Plants, trans, by Ewart, 1900-6, i, 473), in 

 referring to the soluble starch in Saponaria, etc., states that 



Similarly, the cell-sap in the epidermal cells of Arum italicuni turns violet when treated with 

 iodine, the color disappearing on heating and returning on cooling. The substance giving this 

 reaction escapes from the cells as soon as they are killed, and the watery extract yields on evapora- 

 tion a transparent, slightly gummy residue, which turns violet or blue with a watery solution of 

 iodine, but reddish-b^o^vn when alcoholic iodine is added, turning blue in the presence of water. 

 After prolonged boiling a more reddish reaction is given, and also partial digestion with diastase or 

 ptyalin, while ultimately the color reaction disappears, a reducing sugar being formed. This "sol- 

 uble starch" has a very much feebler osmotic value than cane sugar or dextrose, and its molecule 

 is presumably large and complex. Its peculiar distribution points rather to its possessing some 

 biological function (hindrance to transpiration, protection, etc.) than of its having any special 

 value in nutritive metabolism. It may occur in small quantity in the cell-sap of the guard-cells of 

 the stomata, though it seems always to be more abundant in the surrounding epidermal cells, and 

 it may be still present in almost undiminished abundance after a prolonged sojourn in darkness 

 (ten days), although no starch is then present in the mesophyll. The soluble starch soon escapes 

 from the epidermal cells when placed in 50 per cent alcohol, and the same also occiu-s in absolute 

 alcohol, though more slowly. 



Incidentally in this connection might properly be mentioned the discovery of Weder- 

 hake (Centralbl. f. allg. Path. u. path. Anat., 1905, xvi, 517) of the occurrence of what he 

 terms genuine starch-grains in the human secretions and excretions. The so-called starch 

 was found in the fresh spermatic juice and in the testis, and also in a gonorrheal discharge, 

 sputum, tuberculous sputum, pus, and both normal and abnormal urine. The grains yielded a 

 deep-blue reaction with the tincture of iodine, and lost their color upon heating and recovered 



