78 THE MICHIGAN ACADEMY OP SCIENCE. 



THE REGENERATION OF t^EEDLING ROOTS AFTER SPLITTING. 



LURA A. WARNER. 



(Abstract.) 



For the experiments on regeneration I have used the seedling roots 

 of Vicia faba, chosen from a number of species upon whicli I operated 

 with less favorable results. 



These roots are split with a sharp scalpel when they are 2-3 c. m. in 

 length, for a distance varying from 1-5 ni. m., are then repotted in damp 

 sawdust or put up in damp chambers and alloAved to continue their 

 growth. 



While the process of growth and regeneration is going on individuals 

 of the set are removed at intervals and sectioned to determine the 

 anatomical structure of the regenerating tissue. Over the cut surface a 

 callus is cut off from pre-existing cells of epidermis, cortex and stele. 



In splitting, the arrangement of tissues is broken up. Cross sections 

 become half-moon shaped instead of circular. The circles of epidermis, 

 cortex and stele are halved, and the number of bundles is one-half that 

 of the normal section, if the splitting divides perfectly. The half-moon- 

 shaped cross section becomes rounded out by the formation of callus over 

 the cut surface. Across this callus a new meristem arises which joins 

 with the primary meristem and these cells take up the work of regener- 

 ation. Cortex cells are cut oft" on one side and pith and bundle cells on 

 the other. 



For a distance of 1-3 c. m. below the union of the split halves, however, 

 the normal condition is never restored. This intervening piece between 

 the normal condition above the split and the rounded portion below is 

 called the "Zwischen stfick" and in cross section always retains the char- 

 acter of the cut half. 



In this Zwischen sttick the bundles are massed together, primary and 

 secondary tissue in a disorderly manner. 



Below the Zwischen stiick the bundles separate and assume a sym- 

 metrical arrangement, although the number is rarely normal. 



Vicia faba roots contain from 4-7 bundles under normal conditions, 

 but after splitting, only three take up the work of the root system. 

 Otherwise the "regenerated"' root is perfectly normal, splitting only hav- 

 ing reduced its number of bundles and retarded its growth slightly. 

 Since each split half contains three bundles the root system has gained 

 two bundles, if the norinal number were four. 



Perhaps this process should not be called regeneration, but it comes 

 the nearest to the regeneration known in the animal world of any case yet 

 cited. 

 LuRA A. Warner, 



Botanical Laboratory, University of Michigan, 

 Ann Arbor. 



