350 Colchicine 



parts and leai. Since the cells ot the first layer at the aj^ex always 

 divide anticlinally and not periclinally, all epidermal cells trace their 

 origin back to the first layer as seen in the shoot apex. Accordingly, 

 the second layer divides anticlinally, and tissues originating from 

 the second layer will be independent in genetic make-ui) from the 

 first, and in many cases from the third. If colchicine changes the cells 

 of the first layer to tetraploidy while the second layer remains diploid, 

 then the epidermal cells will be tetraploid and the pollen grains dip- 

 loid, because the sporogenous tissues originate from the second 

 layer. This condition is called a periclinal diimcra. Various com- 

 binations can be had. 



When geneticists realized that the treated plants might look like 

 tetraploids yet reproduce as diploids, the significance of periclinal 

 chimeras began to be tridy appreciated.'^' '^ Moreover, developmental 

 problems can be traced with closer attention to the origin of tissues, 

 because specific periclinal chimeras shoidd yield certain results in 

 the matme organs.^-- ^•*- ^^ If the pollen develops from the second 

 layer, T^, just beneath the epidermis, which is T,, then diploidy and 

 tetraploidy will be loiuid in pollen and epidermis according to the 

 changes in T^ and T-,. I hat is to say, a tetraploid second layer, Tj. 

 should produce tetrajjloid pollen mother cells while diploid guard 

 cells originate from tliploid Tj. The situation has been j)ro\ed to be 

 ijust that way. These are periclinal chimeras. 



; An important series in Datura was clearly described showing that 

 the development of petals, sepals, pistil, ovules, and stamen coidd be 

 traced back to specific layers of the apical meristem. Similar periclinal 

 chimeras were found in the cranberry. i" Cyto-histological changes 

 were described in detail. One important conclusion "was reached. 

 Stem and lateral bud apices were seldom converted into total poly- 

 ploidy. Therefore, semiwoody and woody plants propagated follow- 

 ing treatment with colchicine, required special attention ^vith care 

 given to the nature of polyploidy induced."' Periclinal chimeras fol- 

 lowing treatment with colchicine have been reported many times 

 since the first cases were reported for Datura.^-- ^•'' 



By induced polyploidy, specific and discrete layers were demon- 

 strated for Datura sirainoiiiuni L.^- The leaf and flower were traced 

 back to the shoot apex. One important type useful in detecting 

 origins was a diploid outer layer, an octoj)loid second layer, and a 

 diploid third layer. ^- Any tissue that originated with an octoploid 

 layer was unquestionably marked by the size of cells. Development 

 of the carpel was traced in Datura^- The periclinal chimeras Avere 

 used to discover specifically how the style, stigma, calyx, and corolla 

 differentiated. In questions regarding axial or foliar origin for such 

 parts as the stamen it can be stated more precisely how development 

 takes place. 



