( 41»7 ) 



Tliis is llio saiiH' xaliic ns wc liiid Uw llic [(rcssiirc cNcrcistMl oii 

 ;i solid, iiiiiii(i\ iiiu' wall. 



ill order lo calciilalt' llic iiiiiiihcr n\' collisions wc Irnc licrc 

 iicLilccIcd llic cxlciisioii of llic iiiolcciilc and llic innlnal allraclioii of 

 llic niolccnlcs. riicrcfoiM' il is a|»|iarciil llial wc caniiol liaxc oltlaiiicd 

 aiiNlIiiiiLi' else Itiil a lirsl a|i|»ro.\inialioii. 



Botanies. " />/V N/rA7/-7'//r^*r/V". l)isserlalioii of Mr. .1. ( '. Sciioi tk. 



^('oiiiinniiicalioii of l'rof. ,1. \V. .Mom,). 



Accordiiiu' to llie idea of \ AN 'l'ii'',(;iii'',M, L>i\'eii al)oiil llie li>siics of 

 i'oot aiul slem of llic \ascnlar planls, lliev iiinsl l»e dixided iiilo lliree 

 uroii|»s or svsicins of I issues, namely, epidei'iiiis, coi-Uw and ceiilral- 

 (wlinder. Il is siicli a natural llii]i,u' lo call llie epidennis a sej)ai'alc 

 lissne llial already a lon,ii' ''"'<' Ix'forc \ an Tik(;iikm. il was ackiiow- 

 lediicd and is al presciil generally accepled. 



Il is a dilferenl lliinu' ahoiil llie llieory llial llie ciMilral |)arl of 

 slem and rooi is taken iip l)y a cylinder of lissiie, llie central-cylinder 

 (or •■stele"), wliicli may consist of elements dillerinu' ,Lireally. l»iil 

 which must iKwerlheless he reuarded as a cojinecled w hole, formiiiii' a 

 certain contrasi with resjiect to the cortex. This consi<leralioii which 

 can he ('idled the " Stelar-lheory "" is acceple(| \)y sinne. rejected 

 hy others. ll is of the urealesi importance for inslrnclion aii<l for 

 the conslriiction of descriptions of the inner slriiclnre. and il has 

 iindoiihtedly for both these i-easoiis such a .u'l'eat practical wciülil. that 

 for this reason only il deser\'es onr atleiition in a liiiili deiiree. 

 'Pile scieiililic foundations for lliis theory ar<' not in Mich a uood 

 condition and assuredly its iion-accej)laiice is ow inu' to this. ( )f course 

 the imporlanl (piesli(ui is. whether lliis distinction helwceii corle\ 

 and central-cylinder has made its appearance already at an early 

 period ill llie phyloLi'eiiy of plants. \\\\]\ the |n-eseii1 slale of our 

 knowledLic lliis can perhaps nol he pro\'ed with certainly: hiil lo 

 lie ahle to answer llii> (pieslion in the af(iriiiali\'e two conditions 

 iiiiisl he pill: 1^'. Ilie central-cylinder must he indicaled if not in 

 all, slid in llie ureater pari of slems and roots, 2 "^ il iiiiisl appear 

 ali-eady at an early period in the (le\ (•lopmeiil of these origans. 



.Vs lor ihe root lliese conditions are amply salislied. which üi\'cs 

 ureal siipporl lo ihe theory of \ \N Tii'.cni'.M. I>iil lliis is not the case 

 lo such an exieiit for the slem, partly perhaps in coiineclioii willi 

 the eumplicalioiisi foniied tilready al an early period \)\ ihe develop- 



