METABOLIC PROCESSES IN THE PLANT. 311 



starch chiefly in the neighbourhood of the vascular bundles, but 

 also in the rest of the parenchyma. When much starch appears in 

 the seedlings from oily seeds, the cotyledons also, which in the 

 dormant seed are free from starch, for the most part contain at the 

 commencement of germination large or smaller quantities of starch, 

 and the non-nitrogenous bodies travel in the form of carbohydrate. 

 If, however, fat migration is exhibited {e.g. in Linum), then the 

 cotyledons are always devoid of starch, and in the other organs 

 also of the seedlings carbohydrates are for the most part present in 

 only trifling quantity. 



1 See Sachs, Botan. Zeitung, 1859, p. 177; also Detmer, Vergleicliende Physio- 

 lofjie des Keiinungsprocesses tier Samen, 1880, p. 316; and H. Schmidt, Flora, 

 1891, pp. 320, 342, and 344. 



123. Germination of the Seeds of Phaseolus nmltiflorus. 



A very favourable object for the study of a series of metabolic 

 processes, and also of many phenomena connected with the trans- 

 location of substances in plants, is the germinating seed of the 

 scarlet-runner (Phaseolus multiflorus). 1 The seed-coat of the 

 bean, as we can easily satisfy ourselves by studying transverse 

 sections, is made up of four layers. The innermost consists of 

 compressed cells ; then follows a layer, several cells thick, of 

 Avhich the cells, in variegated seeds, contain a red pigment. This 

 is followed by a third layer, consisting of very small cells ; and 

 lastly we have a palisade layer, the elements of which are elon- 

 gated in a direction at right angles to the surface of the seed, and 

 have strongly thickened walls. Groups of the palisade cells 

 contain a black pigment, from which the seeds derive their spotted 

 appearance. To obtain good preparations from the seed-coat it is, 

 in my experience, advisable to first soak the beans for twenty-four 

 hours, and then let them dry for twelve hours. Material prepared 

 in this manner serves well for the preparation of thin transverse 

 sections of the seed-coat. The seed-coat surrounds the embryo, 

 which consists of two cotyledons and the axis (root, hypocotyl, first 

 stem internode, and terminal bud), with the two primordial leaves. 

 We easily satisfy ourselves that the cotyledons, being concave on 

 their inner sides, leave between them a cavity, and that the axis of 

 the embryo is bent to form an angle. 



The cotyledons are made up of the epidermis, the largely 



