METABOLIC PROCESSES IN THE PLANT. 317 



teids are found in a state of migration in the soft bast of the 

 bundles. The cambium, the growing points of the stems, and the 

 primordia of the adventitious roots, which originate in the inter- 

 nodes, and which, as I have often found, do not in shoots 

 developing in dry air break through the epidermis, oniy contain 

 proteids, which is, in fact, in accordance with a general rule that in 

 tissues, e.g. the cambium, whose cells are in a very active state of 

 division, carbo-hydrates cannot be detected, because of the ex- 

 treme rapidity with which they are consumed. I do not here 

 enter into farther details, which, however, are easily made out. 1 

 See also 126. 



1 See H. de Vries, Landwirthschl. Jalirbiicher, Bd. 7, p. 217. 



126. The Influence of Temperature on the Amount of Sugar 

 in Potatoes. 



The study of potatoes as regards the quantity of sugar which 

 they contain presents great interest, since investigations of this 

 kind give results which are of value in examining quite a series of 

 physiological questions. We proceed as follows : After rubbing 

 down the potatoes (say four) on a grater or by means of a broad 

 file (rasp), to a fine pulp, we place this on a piece of boiled linen 

 lying in a large porcelain dish, and squeeze out the juice with the 

 hand. We rinse the grater or file, and also the hands, with water, 

 and mix the rinsing water with the pressed residue of the pulp, 

 again squeeze, and repeat these operations twice more. The fluid 

 obtained is run into a flask of half a litre capacity. We fill this 

 up to the mark, and treat a certain quantity of the fluid with 

 Lead acetate to precipitate the proteids, etc., filter, and determine 

 the sugar in the filtrate by means of Fehling's solution. Potatoes 

 just matured contain sugar. If we examine ungerminated pota- 

 toes which have been kept for some time (a few weeks) in a warm 

 room, at a temperature of 15-20 C., we find that they do not 

 contain sugar. If such potatoes, devoid of sugar, are placed for 

 about fourteen days in. a place (say a cellar) whose temperature 

 does not sink below C., but still does not rise above 2-3 C., 

 they become sweet, and contain a good deal of sugar. It is very 

 desirable, in investigating the effect of cold, to put the potatoes in 

 a thermostat placed in the cellar. The apparatus consists of a 

 double-walled zinc vessel. The space between the walls is filled 



