235 



pauses for certain abnormal formative processes. The fact that 

 very different methoas of experimentation Bllow the same speci- 

 fic cause to come into action makes necessary a differentiation 

 between the means used by the experiraentor and the specif ic 

 causal factors , when judging of each abnormal format i on. 



She demands made herewith in the treatment of developmental— 

 meehantoal questions have sis yet been only incompletely satis- 

 fied. Our knowledge of cell-physiology is proved to be insuffi- 

 cient tn every way, HJe can let our glance wander over a mighty 

 field of work, which begins to be passable in only a few paths. 



We will now pass ove* to the special discussion of the 

 different active factors and will briefly explain the special 

 ferm of their action by a number of examples, 



1, Influence of Mechanica l Pressure an d Strain 



" w m i^W <^ ■ .lo w i 1^ ■> ■! .. „ >i,«..>i.ii ■ ■■pwi M - w . i n i'«ii^>i- ■— ii«.-i..« wii^^i ■■II' p' H 'i M l.*! 



5Jhe effect of mechanical pressure ^nd strain on living 

 plants and especially On the formation of tissue, may be con- 

 sidered from different points of view, 



Porce effect alone Is present, when, for example, through 

 pressure, the elements of a tissue are changed from their normal 

 position and are twisted and bent» Tissue characterized by such 

 twisted cells are discussed on p«- li'T. Again, f otf ce effect is 

 present when the elements, attacked during grovrth, are kept 

 from further enlargement. The inhibition of gror/th alone natur- 

 ally does not of itself cause the formation of abnormally con- 

 structed tissue. If the cell division continues its course in 

 arrested grov/th, abnormally small-celled tissue ds produced. 

 In fact s uch may be produced, when (by means of a plaster ban- 

 dage) the objects under investigation are subjected to a suffi- 

 ciently strong pressure (see above p. 29), 



Thus we are concerned with stimulus effect , not only when, 

 by mechanlfial pressure and strain^ the cells are Incited to 



growth or division or special processes of differentiation, 

 ut also when certain forme-tive processes are in any way in- 

 fluenced in their direction by the fi^otors mechanically effec- 

 tive. 



Examples ef this directive influence of pressure and strain 

 will be found In Kny's reports. Under the Influence bf mechani- 

 cal pressure the raeristem cells of the medullary rays in 

 branches of Sallx and Aesculus divide in a different direction 

 than under normal conditions. Double rowed medullary rays are 

 produced^* It seems to me that a case studieid by Klebs belongs 

 f2V6) here (fig. 56). If the walls of the cells of Hormidium are 



made Inoapgble of any further surface grc th (by treatment vdth 

 Congo red), abnormal effects of pressure will be exercised on 

 the grov/lng protoplasts which are enclosed by them. It is very 

 probable that these abnormal pressure cgnditions cause the ab- 

 normal direction of the new cross-walls'*. It does jiot seem 



^ Ueber den Einfluss v«n J>r\icik %f%VLg» u. s« w, pringsheim^s 

 Jahrb, f, wiss. Bet,, 19S1, Bd, mtfXl, p. -6B. 



Oompate alse ab^ve p, 16(?, 



