WOUND-CORK AND CALLUS 



37 



ah df 



o 



Fig. 19. Callus 32 days old on 

 cutting of Hibiscus reginae. a, cor- 

 tex, b, pericycle. c, bast, d, wood. 

 f, xylem parenchyma, g, medulla. 

 h, generative layer, i, n, o, cambium 

 cushion on bast, medulla, and wood. 

 k, parenchymatous tissue of callus. 

 m, cork. After Belzung. 



entiated first while the callus is forming over the wound, and then 

 later a cambium layer is developed from which wood and other 

 tissues may be formed. The tissues 

 formed from the callus do not form 

 a complete union in most instances 

 with the injured surfaces, hence the 

 marks of old wounds may be found 

 beneath the surface of the plant in 

 the wood, especially. In the proc- 

 ess of grafting in which a twig of one 

 plant is fastened with its wounded 

 surface in contact with the wounded 

 surfaces of the stem on which it is 

 to be grown, the two are welded to- 

 gether by the union of the callus 

 which is formed by both. It is im- 

 portant that the tissues in the united 

 elements should show a fairly simi- 

 lar structure and arrangement in order that grafting may be 



readily accomplished, hence the diffi- 

 culty that arises in grafting between 

 species of different genera, which how- 

 ever has been accomplished (See graf- 

 ting.). 1 



55. Formation of Wound-cork and 



Callus. Make a number of cuttings of 



Coleus and Begonia and imbed in 



20. Formation of cork dishes of sand (See cuttings). Take 



in the outer region, of callus of Qne ^ ^ week ^ and make 

 Hibiscus reginae (See rig. 19). 



a, parenchymatous tissue, b, longitudinal sections through the por- 

 phellogen. c, cork, d, epidermal tion ending in the cut surface. Make 



layers of callus. After Belzung. Qut the progress of the formation of 



a special tissue to protect the exposed part of the stem. Ex- 



1 Tittman, H. Physiologische Untersuchungen ueber Callusbildungen und Steck- 

 lingen holziger Gewacb.se. Jahrb. Wiss. Bot. 27 : 164. 1895. 



Fig. 



