229 



thP on!?L''S''^JJ''^^^?"°''^^^'' "-^^^^ ^^y alteration becomes 

 a^^ Zl^ln.^ stimulation lio either in the outer ;7or}d or 

 of f hp^pl??^ i? *^% ^"^^^i°^ °^ «^e orer-nisiii hy the activity 

 ?Lto^^ t^i? K^^?'?^iy^^-. A«°orclingly. external and internal 

 factors must be distinguished:- in their action ;7e speak of 

 external and i nternal stimuli . ' "i'«=^^^ "i 



^"i^r^.■^^^.^?^°^^^ germinate when placed in a nutrient solu- 

 ^?;?^^L^!^«;^^ ^^""^ tube growing out of the roundish spore. 

 n?ifJ!^^''°'^^''°L°^ S^^'^"*^^ ^^^^ °^^-^^e ^- ^03rm is caused by the 

 Sin^oo .^''^' ^" the conditions, to the action of which the 

 m??e thP L^«2°^2^ ?°"*^'^°^ ^ith the nutrient fluid and even 

 more the endosmotic absorption of water and nutritive sub- 

 stances act as stimuli, the reaction of which is recognlzane 

 7= the phenomena of germination. If the- short germinating tube 

 as left under similar conditions, still further change takes 

 place; the sm§ll germinating thread becomes steadily larger 

 am 13 divided by oroas-walls into several cells. These forma- 

 tive processes are also stimulus effects, to be sure, the exter- 

 nal conditions hafe not been changed, but the factors acting 

 on the cells themselves are different* Each enlargement of the 

 germ tn^e results In changes in it which may be found in a dis- 

 ^o<o^ P^J^'^^^^t of the separate particles, in changes of the cheraioal 

 \iitiV) nature of the cell contents, variations In circulation and os- 

 motic pressure, in changes of tension conditions etc. The con- 

 tinuous alteration in the internal factors furnishes an unin- 

 terrupted chain of stimuli to which the organism responds ,. 

 equally uninterruptedly with typical reactions. If we resolve 

 the processes qf development of the growing germ tube into 

 Inntanerable differentials, each of these represents the reac- 

 tion to a definite stimulus; their sum furnishes a continuous 

 process of growth and formation. 



Formative processes - amon^ which we must unconditionally 

 Include the continuance of a process of growth, which has be- 

 gun already - can therefore result from external as well as 

 internal stimuli, iTithout a change in some factor, - external 

 or internal - no process of gro\Vth and forrar.tion is conceivable;- 

 nothing is produced "of itself", nor does it change "of itself". 



Even if the beginning of a process of gror/th, just as 'its 

 continuance, be conceived of as due to the stimulus effect, 

 still an essential difference exists between the two processes. 

 We v^ill wish to mark this difference by terming " reotipetiye 

 Stimuli " those v/hich cause the continuf^.tion of formative pro- 

 cesses already begun, and formative or moryhofienio , the ones 

 which quaihitatively introduce new fornrntive processes. Justi- 

 fication of this distinction vp.y be foimd in the importance of 

 the latter in the maturing of animals and plants. On the other 

 hand, the near Relationship between rectipetive and formative 

 stimuli of formation are involved; they are all formative in 

 the broadest sense of the word. In rectipetive processes of 

 stimulation, the stimulatory cause apparently lies in the 

 changes in internal factors; in the formative ones it must usu- 

 ally be sought for in a change in the coBperative action of 

 external factors, \7ithout any change in the internal and exter- 

 nal factors; i. e. v/ithout some stimulus - this must be re-em- 

 phasized - neither a rectipetive nor a formative process of 

 growth is conceivable. 



On this word compare Virohow, Ueber Reizung and Erizbar- 

 ~ ■ " ' V, p. 1, Billroth, Ueb. d. 



Tie^^ellen aufeinander. Wien 



keit. Sein Archiv. 1858, Bd, XIV, p. 1, Billroth, Ueb. d. 

 Einwirk, lebender Pflanzen- und Tier^ellen s 



1890. Herbst, Xoc, cit. 



