272 The Phenomena of Morphogenesis 



found some types in which (like those examined by Einset) the layers 

 are 2n, 2n, An. In others, these are 2n, An, 2n, the whole core being 

 diploid (Dermen, 1951). He has also studied chimeras in the cranberry 

 (1947a). Einset and Lamb (1951) conclude that most of the so-called 

 tetraploid grapes are actually diploid-tetraploid periclinal chimeras, as in 

 apples. 



Fig. 10-4. Portion of carpel wall and placenta of Datura in a periclinal chimera that 

 was 2n, 8n, 2n in constitution. In material like this it is possible to trace the origin 

 of tissues from specific layers at the meristem. (From Satina and Blakeslee.) 



Kerns and Collins (1947) obtained chimeras in pineapple with col- 

 chicine. Some had a 2n epidermis with all the other tissue An, and these 

 resembled the completely tetraploid plants. Some had a An epidermis and 

 the rest In and resembled completely diploid plants. These authors be- 

 lieve that there are only two "germ layers" in the pineapple. 



Periclinal chimeras have made an important contribution both to 

 morphology and morphogenesis by making it possible to trace the con- 

 tinuity between the regions of the meristem and the structures of the 

 mature plant, since when the cells of the components of a chimera are 

 distinguishable, their descendants can be traced throughout develop- 



