V CELL DIVISION 771 



grape stem and artichoke tuber {Helianthus tuberosus) all behave in the same way. 

 The modified, auxin-independent tissues were called accoutume or adapted. Bioassay 

 of extracts from them shows that they now contain auxin in appreciable amounts 

 (Kulescha 1951). When these accoutume tissues are cultured on media containing 

 auxin, not only is their growth not promoted, but above about o. i mg/1 lAA it is 

 actually inhibited (see Fig. 6). 



Special interest is attached to the comparable behavior of crown gall. The 

 original galls, which contain the causative bacteria, Agrobacterium (Pseudomonas) 

 tumefaciens, give rise to secondary galls free of bacteria; bacteria-free gall tissue can 

 also be obtained by exposure to high temperatures (White and Braun, 1942). This 

 bacteria-free gall tissue grows well on nutrient media free from auxin and shows 

 no growth promotion, but rather some inhibition, by added auxin (Fig. 6). Bioas- 

 say shows it to contain considerable amounts of an auxin (probably lAA), indeed 

 generally more than i\\G: accoutume t\%?,Vi€: (see Table 3, p. 761). Thus the change in the 

 accoutume tissue has been in the direction of the properties of the crown-gall, which 

 are those of a tumor. The change is spontaneous and involves no marked increase 

 in growth rate, only the acquired ability to dispense with the critical growth factor, 

 auxin. Whether this means the gain of the ability to synthesize auxin, or the loss 

 of the ability to destroy it, is not clear, since the destruction occurring in normal 

 tissue may be quite slow (Piatt, 1956). 



It should be made clear that crown-gall is a complex tissue. It contains both 

 large and small cells, cells with thickened and lignified walls and cells which are 

 necrosing. In tissue culture the different galls become very similar {cf. De Ropp, 

 1950) but in situ they retain considerable individuality (Kupila, 1956 and literature 

 there cited). Their growth cannot, therefore, be regarded as a measure of pure 

 cell division. 



Not uncommonly tissue cultures vuidergo multiplication of chromosome strands 

 or even of whole chromosomes, without cell devision. Giant lobed nuclei 

 result, which in one case were calculated to be 128-ploid (Therman, 1951). 

 Binuclear cells, each nucleus of which is polyploid, also occur (Skoog, 1953). In 

 tissue cultures of fern prothallia, by contrast, the chromosome number builds up 

 gradually in successive transfers. Chromosome counts and microchemical DNA 

 determinations agree in showing small, more or less random, increments reaching 

 3 [jL or 4 [J. ; along with these nuclear changes there is a morphological change 

 away from typical prothallus tissue toward a tumor or callus type of growth 

 (Partanen et al., 1955). Prothallia in which the nuclei remained normal continued 

 to grow as recognizable prothallial tissue. 



The formation of roots on stems, as in the rooting of cuttings, begins with cell 

 division in the pericycle or phloem parenchyma, as was first shown by van Tieghem 

 in 1888 and has more recently been demonstrated in several plants (Reano, 1940; 

 McDaniels, 1955) and this process in the majority of plants is also stimulated by 

 auxins. For woody tissues lAA, NAA or IBA at 100 mg/1 is applied to the base 

 of the cutting for 18 h, while for soft green stems 1-5 mg/1 may be as much as can 

 be applied without damage. Although too long a period of application may 

 inhibit the subsequent elongation of the formed roots, there is no evidence that it 

 inhibits the initiation process. The response of cuttings varies with the part of the 



Literature p. 816 



