METABOLIC PROCESSES IN THE PLANT. 293 



- See Eriksson, Unters. a. d. bot. lust, zu Tiibint/en, Bd. 1. 

 3 See Dutrochet, Annal d. sc. nat., 1840, Ser. II. T. 13, p. 5. See also 

 Pfeffer, Handbuch, Bd. 2. 



III. THE BEHAVIOUR OF NON-NITROGENOUS PLAS- 

 TIC SUBSTANCES IN PLANTS. 



110. Starch as Reserve Material. 



In very many receptacles of reserve material, the non-nitroge- 

 nous substances are laid down in the form of starch. We may 

 satisfy ourselves of this by mounting in water, and examining 

 under the microscope, delicate sections from the cotyledons oL r 

 peas or beans, from the endosperm of a wheat grain, from a potato, 

 or from a rhizome of Canna indica. The starch grains in the cells 

 are easily recognised, and for confirmation we may stain them blue 

 by means of Iodine. Even in the medullary rays, and in the wood 

 of trees and shrubs, starch is very generally stored up during the 

 winter as reserve material. 1 I obtained particularly good results 

 with twigs of Berberis vulgaris, Fraxinus excelsior, and Fagus 

 sylvatica gathered in January and February. "We prepare trans- 

 verse and longitudinal sections through the wood of Berberis vul- 

 garis, mount them in a drop of iodised glycerine (prepared by 

 leaving Iodine in glycerine for some time), cover with a cover- 

 glass, and warm the slide over a spirit flame. Microscopic exami- 

 nation after cooling shows that the medullary rays especially, but 

 also the elements of the wood, contain agglutinated "masses of 

 starch, which have stained blue. The wood of Fraxinus consists 

 of broad and narrow vessels, scanty wood parenchyma, principally 

 occurring in the neighbourhood of the vessels, and wood fibres. 

 Transverse sections through the wood, treated as indicated with 

 iodised glycerine, show that it is mainly the cells of the medullary 

 rays which are rich in starch. In Fagus there is besides the ves- 

 sels and wood fibres a fairly large quantity of wood parenchyma, 

 running in tangential bands. This, as also the cells of the broad 

 medullary rays, is very rich in starch. In the spring the starch 

 disappears from the medullary rays and wood of the vascular 

 bundles. Obviously the starch now passes out of these tissues, in 

 which it was stored up as reserve material, and travels to the 

 growing parts of the plants. 



To obtain accurate information as to the starch contents of a 



