CORRELATION AND REPRODUCTION 161 



PART II 



CORRELATION AND REPRODUCTION 

 SECTION 45. General. 



The progress of development of each organ and cell must be so 

 directed by its correlative relationships with other parts as to create and 

 maintain the essential harmonious co-operation of the whole l . Any 

 disturbance must therefore so act as to induce reactions tending to its 

 removal and to the restoration of equilibrium. These self-regulating 

 actions are in constant operation during the normal life-cycle, and are not 

 merely aroused by external stimuli. The reactions to the latter are, how- 

 ever, of importance in affording some insight into the interactions under 

 normal conditions. By analogy with self-regulating machines we can 

 understand that a perceptible reaction may appear only at one point, 

 although the whole organism may be affected by localized stimuli. Finally, 

 correlative influences may affect not only growth, but also the metabolism 

 of growing and non-growing organs. 



The most immediately perceptible formative action due to the influence 

 of correlation is the tendency of pieces of stem and root to replace the 

 missing parts. This tendency is made use of in reproducing plants by 

 cuttings, in which productive activities are awakened in special meri- 

 stematic cells or groups of cells which under the normal relation of parts are 

 kept at rest by functional interaction. This applies to very many of the 

 buds, for if the opening ones are removed the dormant ones begin to 

 develop, and the same occurs when the development of the larger buds is 

 mechanically prevented by the application of plaster-casts 2 . In this way 

 the plant is able to supply any deficiencies, so that a tree acquires fresh 

 foliage when the young leaves are destroyed in spring by frost or insects 3 . 

 This replacement involves either the awakening of dormant buds, or the 

 immediate development of buds which were beginning to form ; and in the 

 latter case the formation of bud-scales maybe suppressed or modified. In 



1 The term correlation is used here in the general sense to include all results, whether occurring 

 in the form of growth or of metabolism. A few pronounced growth-correlations were early noticed. 

 Cf. e.g. de Candolle, Theorie e'l^mentaire, 1819, 2 e e"dit., p. 90; Pflanzenphysiologie, 1835, Bd. II, 

 P- 333 > Knight, Phil. Trans., 1806, II, p. 293. See also Vochting, Bot. Ztg., 1895, p. 79; Goebel, 

 Flora, Erg.-bd., 1895, p. 194; Organography, 1898, I, p. 198; Herbst, Biol. Centralbl., 1895, 

 Bd. XV, p. 721. 



2 Pfeffer, Drnck- u. Arbeitsleistungen, 1893, pp. 357, 382 ; Richter, Flora, 1894, p. 416 (Chara] ; 

 Hering, Jahrb. f. wiss. Bot., 1896, Bd. XXIX, p. 137. 



3 A. P. de Candolle, Pflanzenphysiol., 1833, Bd. I, p. 437 ; Treviranus, Physiol., 1835, p. 299; 

 Nordlinger, Forstbotanik, 1874, Bd. I, p. 156 ; Askenasy, Bot. Ztg., 1877, p. 828 ; Potonie', Sitzungsb. 

 d. Brandenburg, bot. Vereins, iSSo, Bd. xxn, p. 79; Goebel, Bot. Ztg., 1880, p. 804. 



PFEFFER. II ] 



