168 THE CAUSE OF SPECIFIC SHAPE 



further growth. Many flowering plants can reproduce themselves from shoots, stems, 

 or roots, and in certain cases a single resting cell may form the starting-point of a 

 bud and hence of an entire new plant. In other plants this power is less highly 

 developed, and hence it is difficult or impossible to reproduce such plants as 

 Fagus sylvatica and Pinus sylvestris from cuttings. 



Fragments below a certain size are incapable of reproducing a new plant, 

 although Rechinger x was able to attain this with sections of the root of Cochlearia 

 armoracia ij mm. thick, and Koch 2 saw an entire plant produced from a small 

 piece of the suspensor of an Orobanche embryo. It may even be found possible 

 to obtain an entire flowering plant or moss from a single embryonic vegetative cell, 

 as frequently occurs in Thallophyta. In Vaucheria, Mucor^ and other multinucleate 

 plants a small fragment of cytoplasm, if it contains a nucleus, may reproduce a new 

 plant 3 . The same power is possessed by nucleated pieces of the zoospores of 

 Vaucheria^ Oedogonium, and other algae 4 , and without doubt the ovum of a flowering 

 plant, like that of certain animals, may be able to develop after the removal of 

 a portion of its cytoplasm. In spite of the minuteness of the ovum, everything 

 necessary for the reconstitution of a new organism must be present in it. 



The pronounced power of repair possessed by plants is closely 

 connected with their ability to accommodate their shape to the external 

 conditions. Thus a plant which normally forms a tap-root system may 

 still be able to develop when, owing to the removal of the main root, or to 

 the character of the soil, it is compelled to form a bushy root-system. 

 Similarly the shoot-system may be caused to assume a variety of shapes. 

 In animals with definite shape the power of reproduction is less 

 pronounced, while plants are able to repair damaged organs just as 

 well as are animals. 



Thorough regeneration takes place in the root of Zea Mays, Faba, &c., if the 

 outermost layer of meristem at the apex is removed 5 . If, however, a piece 

 i to 3 mm. long is removed from the apex, callus-formation ensues, and one 

 of the lateral roots developed from the callus may replace the primary root so 

 thoroughly that the sympodial character of the new axis is eventually no longer 

 perceptible 6 . If a radicle is severed in half longitudinally, full regeneration occurs 



1 Rechinger, 1. c., 1893, p. 321 ; cf. also Vochting, 1. c., 1878, pp. 37, 73. 



2 Koch, Entwickelungsgesch. d. Orobanchen, 1887, pp. 9, 28, 193. Cf. also Vochting, Organ- 

 bildung, 1884, II, p. 22, and the literature quoted by Frank, 1. c., p. 121, and by G. Haberlandt, Schi 

 einrichtung d. Keimpflanze, 1877, p. 79. 



3 Pfeffer, Osmot. Unters., 1877, p. 129; Schmitz, Beobacht. iiber Siphonocladiaceae, 1879, P- 33 

 (repr. from Festschrift d. naturf. Ges. z. Halle) ; Hanstein, Bot. Abhandl., 1880, Bd. iv, Heft 2, p. 46 ; 

 Klemm, Flora, 1894, p. 19. On Mucorineae see van Tieghem, Ann. d. sci. nat., 1875, 6 e sen, 

 T. I, p. 19. 



4 Cf. Hofmeister, Zelle, 1867, p. 74 ; Nageli, Pflanzenphysiol. Unters., 1855, 1, p. 174 ; A. Braun, 

 Ueber d. Erscheinung d. Verjiingung i. d. Natur, 1849-50, p. 174. 



5 Vochting, Organbildung, 1884, II, p. 68. 



6 Observed by Cisielski, Beitrag z. Biolog. von Cohn, 1872, I, Heft 2, p. 21 ; and studied 

 detail by Prantl, Arb. d. Bot. Inst. in Wiirzburg, 1874, Bd. I, p. 546. 



