STRUCTURE OF PLANTS. 55 



glance at the Fig. 2 in PL n, shows, however, at once, 

 that the contents of the outer cells of the nucleus are very 

 different from those of the inner; for while the latter 

 enclose a great quantity of starch and very little nitrogenous 

 matter, in the outer layer of cells we find only the 

 latter substance which, in the cereal grains, usually receives 

 the name of gluten ; thus the anatomical investigation of 

 one of these corn grains at once explains, why bread is 

 so much the less nutritious, the more carefully the bran has 

 been separated from the meal. 



But starch is, after all, the most remarkable substance 

 that we meet with in the cells, not merely because it plays 

 so important a part in the nutrition of mankind, but also, 

 setting that out of the question, on account of the peculiar 

 and elegant forms which it exhibits under the microscope, 

 and which indicate a high degree of internal organiza- 

 tion. 



It occurs in every plant, in every part, but only the 

 roots, tubers, seeds, fruits and, more rarely (as in the 

 Sago palm) , the pith contain it in sufficient quantity to serve 

 as food, or to repay the trouble of separating the starch 

 from them. 



We have to thank an exceedingly curious peculiarity of 

 starch for our power to recognize it in any spot and 

 in the smallest quantity in the interior of plants. This 

 is the sudden assumption of a beautiful violet-blue 

 colour when it is moistened with a solution of iodine. 



Starch itself consists of little shining transparent granules, 

 from twenty to thirty of which often lie in one cell, 

 (PL n, Fig. 2, c.) The separate granules sometimes 

 exhibit a very compound structure. They consist of a 

 small nucleus around which a varying number of layers 

 have been deposited. As these layers are usually thicker 



