312 



BOTANICAL GAZETTE ' [apwi 



rent conceptions of the nature of the cambium products, i. e., that the 

 cambium produces cortex externally to itself, but internally it pro- 

 duces a tissue which he calls the " prismatic layer/ ' and this he regard- 

 as being made up of phloem cells, tracheids, and parenchyma. 

 Hegelmaier (12), writing in 1874, is inclined to question Russow's 

 interpretation, but adds that no decisive grounds can be given again- 

 the interpretation of the Dauerzellen as soft bast. Farmer (9 

 published in 1890 a very full discussion of I. lacustris. He 

 reluctant to accept Russow's theory of the nature of the cambium 

 products, but does not offer another. After quoting Russow h 



H-em- 



Quite 



from 



anomalous, its structure is remarkably complex and heterogeneous 

 In discussing the structure of the "prismatic layer" he says: 



The zone-like arrangement consists in alternations of tubular thin-wa e 

 cell-rows of varying thickness, whose cell contents are clear and water)', WW 

 others, whose cells are wider in the radial direction, and filled densely with stare . 

 Occupying a middle position in the latter zone is embedded an irregular ring 

 of cells whose walls are thickened like those of the tracheids, but these too, un 1 e 

 the latter, often contain protoplasm and starch. 



In 1900 R. Wilson Smith (22) discussed the morphology of . 



tt* 1~v *r*r- 



echinospora, with some incidental work on its anatomy, ws 

 vations do not agree with those of Farmer on /. lacustris, ana 1 

 proposes "to drop the term phloem until its justification is establi^ 

 on physiological grounds." In the same year there appeared a 

 exhaustive paper on /. Hystrix by Scott and Hill (19) • The na 

 of the cambium products was taken up, and Russow's conception w 

 indorsed, in that they regard the secondary tissues interna to 

 cambium as consisting of secondary tracheids, parenchyma, 

 phloem. Their statement is as follows : 



The cambium in J. Hyst 



•lem 



cylinder, continues its activity indefinitely, producing parencnyma, y _ -^ 

 a variable amount of secondary xylem on its inner side, and secon a 



parenchyma only, towards the exterior. 



Each of the last three writers has based his conclusion on tj^ ^ 

 of a single species, while Russow, who investigated three or^ ,^ 

 hampered by the fact that he worked on herbarium materia . 



