TISSUES AND SIMPLE ORGANS. 71 



of scientific botany, and not an elementary presentation. For that 

 reason we must enter somewhat into a discussion of the progress of 

 botanical science as well as of the modern change of opinions. 

 This is important because every modern author of a work on general 

 plant anatomy must harmonize his position with NAGELI'S concep- 

 tions of " xylem " and u phloem." 



SCHWENDENER'S investigations of the mechanical tissue-system, 

 and the attempt made to introduce gradually an anatomical-physio- 

 logical terminology lessened the importance of Nageli's terms, per- 

 haps denied them the right of existence. In spite of this Nageli's 

 terms are still in use, and variously applied by different authors. 



NAGELI proceeded from the cambium-ring of dicotyledonous 

 plants, which grows outwardly and inwardly, therefore showing a 

 bipolar cell-activity. From a purely topographical standpoint he 

 called the outwardly formed product phloem and the inwardly 

 formed product xylem. By applying these conceptions to plant- 

 groups without a cambium-ring confusion arose. It could not 

 be otherwise. At present we are certainly too far advanced in our 

 knowledge of tissues to wish to divide them topographically. 

 Earlier anatomists subsequent to NAGELI observed the occurrence 

 of mechanical cells outside of, as well as within, the cambium-ring ; 

 these authors did not all agree with Nageli to designate similar 

 elements by different names. Further, we very frequently find 

 anatomical elements resembling very closely those occurring in the 

 phloem and xylem, namely, the thick-walled prosenchy ma-fibres of 

 monocotyledons, which occur as rings, ribs, etc., and are independent 

 of any cambium-ring. One investigator may name them " hard 

 bast," another " woody cells," both would be equally correct from 

 an anatomical standpoint. LINK and KIESER (earlier anatomists) 

 pronounced the mechanical ring of Liliacece and other monocoty- 

 ledons to be " bast " ; MOHL questioned the propriety of doing 

 so. DIPPEL named the bast occurring in the vascular bundle 

 "wood," that occurring outside of the bundle bast, though the 

 cell-forms are exactly alike. SCHACHT and UNGER do likewise, but 

 the former questions whether the term wood is here rightly ap- 

 plied. 1 



The author of this book is in a position to make clear the absurd- 

 ity of the earlier conceptions of Nageli. I may also refer to DE 



Compare Schwendener's Mechanische Priucip. 



