Chapter III 

 THE LIVING MATERIALS 



In the chapter on the history of plant tissue cul- 

 ture, data were presented on a long series of at- 

 tempts to grow excised plant tissues. Most of 

 these attempts failed ; a few were successful. If 

 plant tissues are classified according to their ob- 

 served usefulness as culture material, it becomes 

 immediately obvious that all of the tissues which 

 have given promise of being grown satisfactorily, 

 with the single exception of Schmucker's uncor- 

 roborated report (1929, 110) on leaf-mesophyll 

 cells, have been meristematic tissues. With this 

 single exception, all "mature" tissues have failed. 

 This is not to say that they are all incapable of 

 growth. But available evidence seems to indicate 

 that, when a meristematic function is resumed by 

 cells at any point in the plant body, as in the case 

 of healing internal wounds, these cells are for the 

 most part not truly mature (Schilling, 1915, 321, 

 1923, 322 ; Jaeger, 1928, 298) . The medullary ray 

 parenchyma, phloem parenchyma, pith cells in 

 general, pericycle and endodermis, and cortical 

 parenchyma are known to retain their meriste- 



