170 PLANT PHYSIOLOGY 



LEWSKI; and (d) the traction theory of DIXON and JOLY. All 

 of these he should expound clearly in a suitable essay. 



LITERATURE OF TRANSFER. The literature of this perplexing 

 subject was admirably summarized, and the knowledge of the subject 

 discussed, down to 1888 by H. MARSHALL WARD in "Timber and 

 Some of its Diseases" (London, Macmillan, 1889). Since then the 

 most important works have been STRASBURGER'S "Die Leitungs- 

 bahnen der Pflanzen " (of which there is a good review in Annals of 

 Botany, 6, 1892, 217) and the very important works by DIXON and 

 JOLY 'in the Annals of Botany, 8, 1894, 468, in the Proceedings of 

 the Royal Society, 57, 1894, 3, and in the Philosophical Transac- 

 tions, 186, B, 1895, 563. There is a summary of an important dis- 

 cussion upon the subject in the Annals of Botany, 10, 1896, 630. 

 DIXON has recently answered objections and reaffirmed his views 

 in the Proceedings of the Royal Society, 79, 1907, 41. There is a 

 very complete summary of the literature down to 1902 by COPELAND 

 in the Botanical Gazette, 34, 1902, 161, a synoptical summary by 

 WIEGAND in the American Naturalist, 40, 1906, 409, and a brief 

 summary of recent literature by BARNES in Botanical Gazette, 42, 

 1906, 150. 



(b) Translocation. 



Our knowledge of the movements of plastic or food sub- 

 stances through the plant, especially as concerns the energetics 

 of the process, is very incomplete, and the experimental study 

 of the subject is for the most part not profitable for the student 

 of this course. Still he may follow it to some extent through 

 the following suggestions: 



SUGGESTED EXPERIMENTS. Translocation by Streaming. This limited 

 form of transport may be observed in large streaming cells, in Myxomycetes, 

 and in growing pollen -grains. Compare DETMER, 346. Correlated with 

 this are possible movements in the latex system and those due to growth. 



Path of Translocation. This, for the general route, is determined by 

 ringing the bark, i.e., removing a ring all around the trunk, or else by con- 

 stricting it, which results in an abnormal growth, due to accumulation, above 

 the constriction. Compare DETMER, 351. Here belongs also the difficult 

 subject of the relative parts taken by the sieve system, the starch sheaths, 

 and the cortex, in translocation. 



A phase of this subject of special prominence and interest, 

 viz., the translocation of the photosynthate from green leaves 

 into the stem, has already been noted under photosynthesis, 



