316 PHYSIOLOGY OF NUTRITION. 



on a slide, and examine with as strong magnification as possible, 

 we shall find, together with uninjured starch grains, others which 

 owing to the action of the diastatic ferment developed in germin- 

 ating wheat, appear corroded and, as it were, gnawed to pieces. 1 



1 See Sachs, Botan. Zeitung, 1862. 



125. The Germination of Potatoes. 



Potatoes consist almost entirely of thin-walled, starch-contain- 

 ing parenchyma. Not only are the medullary and cortical tissues 

 mostly of this character, but also almost the whole tissue of 

 the circularly arranged vascular bundles is parenchymatous in 

 character, and contains starch grains of various sizes. In the 

 wood of the vascular bundles there are present only isolated 

 groups of lignified elements (vessels and wood fibres), while in the 

 bast occur isolated strands whose cells contain not starch but 

 proteid matter. The cortical parenchyma of the potato becomes 

 smaller celled, and poorer in starch, as we pass from the inside 

 towards the skin. On the other hand, the cells of the cortex, close 

 below the skin, frequently contain pigments, etc., dissolved in the 

 cell-sap. The skin of the potato consists of cork tissue, whose 

 cells are tabular in form. 



I have often satisfied myself that potatoes placed in autumn in 

 a vessel whose cover is not air-tight, do not germinate for a long 

 time. The potatoes under ordinary conditions undergo a period 

 of rest before germination. This does not begin till about the 

 new year, when single buds of certain eyes, especially those in the 

 part of the potato opposite the old point of attachment to the 

 runner, gradually enlarge and grow. We now leave the potatoes 

 in darkness, and without provision of water. At the beginning of 

 March, many shoots of the potato have already become a few 

 centimetres long, and small scale leaves are visible on them. In 

 transverse sections through the stem of the shoots it is easy to 

 make out the epidermis, the parenchyma of the cortex and pith, 

 and the circle of vascular bundles. Applying the usual micro- 

 chemical tests to determine the distribution of material in the 

 shoots at different stages of development, we arrive at the follow- 

 ing chief results. The parenchyma of very young shoots contains 

 much starch. As the cells of the parenchyma become older, and 

 actively elongate, they become especially rich in glucose. Pro- 



