PATHOLOGIC PLANT ANATOMY 38 1 



processes which result in the formation of the vegetative points of roots 

 and shoots following an injury. Following an injury in very many 

 woody plants, there is a formation of adventitious roots and adventi- 

 tious shoots which grow from vegetative points developed directly 

 from the permanent tissue of the wounded plant organs, but this opera- 

 tion is necessarily preceded by formation of callus and in some cases 

 the new vegetative points are developed directly from the callus. 

 Upon these functional operations depend the success of the horticultural 

 operations of the making and establishment of cuttings of roots, stems, 

 and leaves. A very large number of plants may be raised by means of 

 cuttings. Soft-wooded, or herbaceous cuttings having leaves are used 

 in many cases, the shoots being in a half-ripened condition, that is 

 neither too young nor too old, dry and woody. Such cuttings are 

 usually inserted in sandy or gritty soil, and most of the leaves are 

 stripped off to check transpiration of moisture. Several leaves are 

 retained, so that a certain amount of assimilation can be carried on to 

 induce callus formation. 



WOUND-WOOD 



The wood, which is formed on the surface of the exposed wood of 

 the stem and on the inner surface of the detached bast, is distinguished 

 from ordinary wood by its abnormal structure, and especially by the 

 shortness of its cells and the absence, or scarcity of vessels. Hugo de 

 Vries,' who was the first to direct attention to this abnormality, called 

 such wood, wound-wood. Such abnormal wood is distinguished from 

 the normal xylem by its simple histologic character, and is to be added 

 to the list of cataplasms. 



The difference between wound-wood and normal wood depends 

 upon whether its formation has been brought about by cross cuts into 

 the cambium, or by longitudinal wounds. In the latter, the wound- 

 wood is distinguished by a wide-celled structure and by more numerous 

 ducts than in normal wood, but the libriform fibers are less in evidence. 

 Hugo de Vries studied Caragana arborescens and proved that the 

 wound stimulus caused the formation of wound tissue 7 cm. from the 

 wound itself. The nearer the cells of the cambium are to the wound 

 the more cross walls are formed, so that the short-celled zone of the 

 ' DE Vries, Hugo: Ueber Wundholz. Flora, 1876: 2. 



