SUPPLEMENT 97 



conjunction with others ; we regard these capacities in the normal condition 

 as being correlatively inhibited. 



Before proceeding to discuss the regeneration phenomena in larger organs, it 

 must be briefly noted that there are other ways besides plasmolysis of separating 

 a tissue into its individual units. In many Marine Algae the thallus breaks 

 up into smaller branches, and even into single cells, when the culture conditions 

 are unfavourable, and TOBLER (1906) has observed regene ration phenomena 

 in single cells of Griffithsia schousboei similar to those described in Cladophom. 

 In higher plants HABERLANDT (1902) has isolated assimilatory cells by teasing, 

 and has cultivated these cells in various nutrient solutions. He found, how- 

 ever, that the resultant growth was only limited. WINKLER (19020) has 

 isolated cells of higher plants in other ways, and was able to observe growth 

 and division also, after adding small doses of certain poisons to the culture. 

 No regeneration phenomena of any kind, however, are exhibited by cells so 

 differentiated as these. Isolation of larger parts of the entire plant is effected 

 by sectionizing, involving the infliction of a wound. The first result is always 

 an effort on the part of the plant to heal the wound. 



1. 46, after affected read (comp. MASSART, 1898). 



328, 1. 14 P. 329, 1. n, for This is, however, ... of this tree, read Other 

 substitutional growths, however, also arise from callus, which are always of 

 such a character as to replace the lost members. According to the way in 

 which this takes place we may distinguish several types of regeneration : 



1. The lost organ is replaced by a new one formed from the cortical region 

 of the lesion, and at the same spot. 



2. The new organ arises in the neighbourhood of the wound, or in the 

 callus arising from it. 



3. The new organ is derived from primordia previously developed in the 

 neighbourhood of the wound. Unfortunately the terms regeneration, repro- 

 duction, restitution, separation, have been applied by different authors to these 

 various types of regeneration (linked together as they are by transitional forms), 

 and that too in very different senses. It is perhaps preferable to apply the 

 term regeneration to all three types, and to describe the first as restoration, 

 the second as renovation, and the third as replacement. 



Examples of restoration are comparatively rare in the plant world ; they 

 are most common at the root apex. If about 0-5 mm. or less of the growing 

 point be cut off (comp. SIMON, 1904), in a few days the apex is restored from 

 cells bordering on the wound. Corresponding results have been observed on 

 splitting longitudinally the growing points of certain ferns (GoEBEL, 1902 ; 

 FIGDOR, 1906), and FIGDOR (1907) has noted the same phenomenon in longi- 

 tudinally cleft leaves of Gesneraceae. Vegetative shoots of some of the higher 

 plants also show a restoration of the missing halves, when these shoots are 

 divided longitudinally (PETERS, 1897 ; KNY, 1905). The power of restoring 

 organs which have been removed is always limited to embryonic tissue, but it 

 is by no means a constant character of it ; it is not possessed, for example, by 

 the majority of fern roots, or of vegetative growing points. 



The second type of regeneration, renovation or re- formation in the neigh- 

 bourhood of the wound, is much more common ; it is so closely connected with 

 the third type, replacement, by transitional stages, that it is difficult to separate 

 them in actual practice. If by primordium of an organ we mean only a cell 

 mass already differentiated, then the two types must always be kept distinct. 

 But there are primordia which, apart from macroscopic and visibly distinct 

 primordia, are only microscopically distinguishable, and, further, even invisible 

 primordia, groups of cells which, externally, give no indication of their capacity 

 for giving rise to the organ in question, but which can perform the duty much 

 JOST G 



