270 The Phenomena of Morphogenesis 



nor 72 chromosomes) can probably be explained in other ways. Brabec 

 (1954) repeated Winkler's work and found cells with varying and 

 irregular chromosome numbers but attributed this fact to the origin of 

 the new shoot from highly polyploid cells. Pith cells, as has been shown 

 by various workers, are often polyploid, and when chimeras come from 

 such tissue the chromosome situation is often complicated. The genetics 

 and .cytology of the Solarium chimeras have been studied by Gunther 

 (1957). Present evidence is against the occurrence of vegetative 

 hybridization and the existence of burdos. In the light of recent knowl- 

 edge of periclinal chimeras, Bergann (1956) has reinvestigated the 

 Crataegomespili. 



Control 2n, 2n, 2n 



8n, 2n, 2n 



4n, 2n, 2n 



2n, 4n, 2n 



Fig. 10-3. Apical meristems of four periclinal chimeras in Datura consisting of 2n, 4n, 

 and 8n layers. Labels refer to the first two layers and the core. ( From Satina, Blakes- 

 lee, and Avery. ) 



In leaf and fruit, the tomato and the nightshade are very different. 

 Each of the four periclinal chimeras produced by Winkler by grafts 

 between them shows distinctive combinations of these traits so that it 

 is possible to determine the effects of one and of two cell layers of each 

 type when it covers a core of the other. Such chimeras provide an excel- 

 lent opportunity to study the morphogenetic influence of the various 

 meristematic layers and the developmental origin of shape differences 

 and of tissues. 



The most complete and thoroughly analyzed series of periclinal chim- 

 eras are those studied by Satina and Blakeslee in Datura (1941, 1943, 

 1944, 1945; Fig. 10-3). By soaking seeds of Datura stramonium in col- 

 chicine solution, polyploidy was induced in certain cells of the shoot 



