162 THE CAUSE OF SPECIFIC SHAPE 



the case of cuttings from roots, buds usually only arise when the correlative 

 influence of an existent shoot has been removed. 



In the same way the formation of roots or the growth of root-primordia 

 may be induced at certain points in cuttings ; and if this is prevented by 

 mechanical or other means, the development may take place at other 

 suitable regions. It is even possible in this way to cause the aerial shoots 

 of the potato and other plants to produce tubers 1 . If only a few shoots or 

 roots are allowed to develop, these usually become stronger. Similarly the 

 removal of the apical growing zone of the main axis causes an accelerated 

 growth in the lateral axes, and at the same time so affects their geotropic 

 sensibility that the lateral branches grow obliquely upwards, the lateral roots 

 obliquely downwards, so tending to replace the main axis. 



Correlative actions of this kind take place in other organs. Thus the 

 individual foliage leaves frequently become distinctly larger than usual, 

 when only a few are allowed to develop 2 , and Hering observed that the 

 removal or imbedding in a plaster-cast of the large cotyledon of Strepto- 

 carpus caused the smaller and usually dormant one to develop into the 

 large foliage leaf formed by this plant 3 . It has already been mentioned that 

 the foliage leaves of certain plants attain a considerable size in darkness, 

 provided those exposed to light are removed. Similarly the stipules of 

 Fdba become considerably enlarged if the lamina of the leaf is removed at a 

 sufficiently early stage 4 . Further dwarf shoots may elongate to replace the 

 ordinary branches 5 , shoots may be replaced by the development of primordia 

 which normally would form thorns, the assimilatory surface of a leaf may be 

 increased by the conversion of the primordium of a tendril into a leaflet 6 . 

 Lastly, the primordia of bud-scales may develop into foliage leaves if the 

 winter-buds are brought to immediate development 7 . 



Since the process of self-regulation involves mutual interactions, 

 a retardation of growth in the shoot involves a slower growth of the 

 root, and vice versa. The same result occurs when the shoot or 

 root-system is entirely or partially removed, and when growth is 

 rendered impossible by imbedding in a plaster-cast. Similarly the 

 removal of the fertilized ovule or ovules inhibits the further development 



1 Knight, Phil. Trans., 1806, p. 298 ; Vochting, Bibl. hot., 1887, Heft 4, p. 25 ; Jahrb. f. wiss. 

 Bot., 1900, Bd. xxxiv, p. i. 



2 Goebel, Organography, 1900, I, p. 210. 



3 Hering, 1. c., p. 142. 



4 Goebel, Bot. Ztg., 1880, p. 838; Organography, 1900, I, p. 2 TO; Kronfeld, Bot. Centralbl., 

 1887, Bd. xxxii, p. 363. Boirivant (Ann. d. sci. nat., 1898, 8 e ser., T. VI, p. 393) obtained similar 

 results by removing portions of the lamina. 



6 Henry, Verh. d. Leopold. Akad., Bd. xi, I, p. 95; Vochting, Organbildung, 1884, II, p. 5 ; 

 Busse, Flora, 1893, p. 164; Raciborski, Flora, 1900, p. 29. 



6 Vochting, 1. c., p. 35 ; Mann, Metamorphose, 1894, pp. 28, 33. 



7 On a similar transformation of bulb-scales cf. F. Hildebrand, Bot. Ztg., 1892, p. 32. 



