312 PHYSIOLOGY OF NUTRITION. 



developed parenchyma, and the vascular bundles traversing it. 

 The epidermal cells contain no starch ; the elements of the paren- 

 chyma, on the contrary, are very rich in starch. Besides starch 

 they contain proteids, as we can easily find by treating sections 

 from the cotyledons with Iodine and Fehling's solution. The cells 

 of the vascular bandies are free from starch, but contain proteids. 

 Delicate transverse sections through the axis of the embryo show 

 that this is made up of an epidermis, cortical and medullary 

 parenchyma, and the intermediate vascular bundle region. The 

 primordial leaves possess stalk and lamina. If a leaf is spread 

 out on a slide in a drop of water, covered with a cover-glass, and 

 submitted to microscopic examination, nerves are seen to be 

 present in the lamina. All the cells of the parenchyma of the 

 lamina are free from starch, but contain proteids. 



If bean seeds are laid in damp soil, germination at once begins. 

 The young plant grows at the expense of the reserve materials 

 present in the cotyledons. We notice particularly in studying 

 the developing seedling's the emergence of the root from the seed- 

 coat, which takes place first, the appearance of the stem, bent afc 

 the tip, the development of the secondary roots, the formation of 

 the root-hairs and of the hairs on the stem, which are not yet pre- 

 sent in the dormant seed, the growth of the primordial leaves, and 

 the differences which are observable between germination in dark- 

 ness on the one hand, and in light on the other, etc. 



As regards the behaviour of plastic substances in germination, 

 the following is specially to be noted. When the root has attained 

 a length of 2-3 cm., many small starch grains are present in 

 the cortex and pith of the root, and of the hypocotyl, while the 

 cells of the axis of the embryo, before the commencement of ger- 

 mination, usually contained but little starch. Glucose occurs in 

 the cells of the corfcex and pith of the axis, as we can prove by 

 treating the sections with Copper solution and potash, while 

 proteids are chiefly found in the vascular bundle region. As the 

 root lengthens in the course of germination, and the first internode 

 of the stem undergoes considerable elongation, the starch dis- 

 appears from the fully elongated cells of the cortex and pith. 

 Thus, e.g., the cells of the cortex and of the pith at tbe base of the 

 stem soon become free from starch, while the cortex and pith of 

 the upper parts of the stem still contain starch. Ultimately, 

 however, this also disappears. Similarly starch also disappears 

 from the primordial leaves as they develop. When the elon- 



