STORAGE OF RESERVE FOOD 24 1 



If at any time a substance in translocation accumulates in a 

 conducting tissue, it may be reconstructed, or condensed into some 

 insoluble form. Starch which is thus formed is known as transi- 

 tory starch. Such accumulations of starch are not to be taken 

 as marking special conducting tissues however, since the accumu- 

 lation may occur in tissues lateral to the main conducting ele- 

 ments, such as the bundle sheath in which the longitudinal trans- 

 location is comparatively slight. 



Movements of sap through dead cells is not affected by anaes- 

 thetics, but is decreased by mechanical compression. On the 

 other hand anaesthetics and lack of oxygen stop the movement 

 of material in translocation through living cells, due probably to 

 alterations induced in the plasmatic membranes. 



308. Translocation of Carbohydrates from Leaves. Expose 

 some plants of Solanum or Cucurbita to strong illumination, under 

 favorable conditions, during an entire day. In the evening test 

 some of the leaves for starch, which should be found plentifully. 

 Cut off a few of the leaves and put in a moist chamber. On the 

 following morning test some leaves taken directly from the plant 

 and those which have lain in the dark chamber for starch. Those 

 attached to the stem will be found to have been emptied of starch, 

 while about the original amount is present in the detached leaves. 

 The test may be made still more striking and conclusive if the 

 leaves are tested for the total amount of carbohydrates present, 

 by the methods described in 220—226. Another interesting ex- 

 ample of translocation is offered by germinating seeds. If the con- 

 tents of the cells of a resting bean are examined, and compared with 

 those of a seedling which has developed the first pair of leaves, it 

 may be seen that a large amount of the food material stored in 

 the seed has been transported or withdrawn, and presumably used 

 in constructing the growing shoot and root-system. 



309. Storage of Reserve Food. Material which might serve 

 as foods is formed much more rapidly than it is used in furnish- 

 ing energy to the plant, or building material for morphological 

 construction. This tendency to accumulate potential in the shape 



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