METABOLIC PROCESSES IN THE PLANT. 313 



gation of the first internode of the stem is completed, its cortex 

 and pith are completely free from starch. Only the very beauti- 

 fully developed starch sheath, which consists of a single layer 

 of cells, and surrounds the circle of vascular bundles, still con- 

 tains starch grains in large numbers. The cells of the pith 

 and cortex, which have lost their starch, now contain sugar, but 

 this also disappears more and more as the germination approaches 

 completion. Proteids are specially abundant in the sieve part of 

 the vascular bundle, as may be determined by means of Copper 

 solution and potash. When the primordial leaves are fully 

 developed, the germination stage may be considered at an end. 

 The cotyledons are almost completely free from reserve materials. 

 Sections treated with Copper solution and potash no longer give 

 a violet coloration, since proteids are not present, but stain light 

 blue. The quantity of starch in the cotyledons is now only 

 trifling. 



The solution of the starch grains in the cotyledons begins as 

 soon as vital activity is manifested in the embryo, and it is indeed 

 those cells of the cotyledons which lie next to the axis whose 

 grains are first attacked. When the first internode of the seed- 

 ling is rapidly elongating, there are already large quantities of 

 corroded starch grains present in the cells of the cotyledons 

 together, it is true, with still uninjured ones, and henceforth the 

 process of starch solution keeps spreading. 



1 See Sachs, Sitzungsberichte d. AkacL d. Wi*s. zu Wien, 1859, Bd. 37, p. 57, 

 and Detmer, Vcryleichende Pliysiologie des Keimungsprocesses der Samen, 1880, 

 p. 308. 



124. The Germination of Triticum vnlgare. 



In order to study carefully the nature of the dormant wheat 

 fruit, we cut sections from grains softened to a certain extent in 

 water. The fruit consists of the pericarp and seed-coat already 

 mentioned elsewhere, and the endosperm and the embryo: We 

 first prepare transverse sections through a grain, and determine 

 that the outermost laj-er of the endosperm consists of a simple 

 layer of almost square cells, whose membranes are strongly 

 thickened, and which have granular contents. Starch grains are 

 not present in these cells, but they contain large quantities of pro- 

 teid, as may be easily ascertained by means of Iodine, or Copper 



