TRANSPORT 171 



where its consideration has some practical experimental value. 

 It may further be tested thus : 



SUGGESTED EXPERIMENTS. Demonstration. The disappearance of starch 

 from unlighted leaves, or their parts, may be shown very simply by attaching 

 a normal screen to a leaf full of starch, say at 10 or n A.M., leaving it for 

 some hours, and later applying the iodine test. This, however, by itself 

 proves only the disappearance of starch as such, and not necessarily the 

 removal of its substance. Here it is important to note the reason for the 

 appearance of the starch at all in the leaf, viz., its use as a reserve form when 

 the sugar of the leaf is accumulating to an osmotically unfavorable amount. 



Amount Translocated. This is very readily settled by use of the leaf -area 

 cutter and method, used in a manner reciprocal to that described for photo- 

 synthesis. 



Relation to Temperature. This is determined, though at expense of much 

 effort, by use of the leaf-area method applied to plants kept for some hours 

 at very different temperatures. Several similar plants are taken when the 

 leaves are full of photosynthate, say at noon ; a number of areas are cut from 

 each one; the plants are then placed for some three or four hours in dark- 

 ness, each in a different temperature; then areas equivalent in number and 

 position to those first taken are removed from them, thus supplying data 

 for a determination of this question. 



A point of practical experimental value in this connection is this: that 

 at high temperatures, say above 25 for most plants, the translocation is 

 so rapid that no starch at all forms in the leaf, for which reason all experi- 

 ments involving starch formation should be carried on at temperatures not 

 above 25, and much better at 2O-22. 



The student should now inform himself through the litera- 

 ture upon the facts o) translocation, including its importance, 

 its paths, and its energetics, the latter involving diffusion, prob- 

 able special pressures, and possible peristaltic actions. 



Closely connected with Translocation is Accumulation of 

 reserve substances, and Secretion of materials of special func- 

 tion already noted in another connection. The student should 

 here work out the method of the transformation of substances 

 from the soluble to the insoluble form, the effect thereof upon 

 the continuity of the diffusion streams, and the physical method 

 by which the substances are removed out of the protoplasm. 



LITERATURE OF TRANSLOCATION. The general works of PFEFFER 

 and of JOST cover this subject well. It comes also very closely into 

 contact with Conversion, earlier studied, and some of the literature 

 there cited (page 121) applies here also. 



