70 



PRINCIPLES OF PLANT-TERATOLOGY. 



long and 7 to 8 millimetres in breadth, and terminated 

 in four rootlets of variable length. 



In P. vulgaris slight fasciation of some of the lateral 

 roots was induced by excising the radicle of the 

 seedling at an early stage of its development. This 

 is a counter- phenomenon to the fasciation of the 

 lateral branches induced by excision of the main 

 plumular axis (PL V, fig. 3). 



2. FUSION. 



POSTGENITAL. 



The facts which are known of the union by natural 

 grafting of two roots belonging to two distinct plants, 

 such as that of two carrots figured by Masters, 

 has, of course, no morphological significance. The 

 same may be said of the similar grafting which 

 occasionally occurs between two bark-forming roots 

 of the same or of two distinct plants as in Ficus 

 scandens, beech, spruce, pine, etc., in which by mutual 

 pressure the union occurs as deeply as the cambium, 

 so that eventually bast and wood common to the two 

 roots is laid down. 



In the ivy and the asclepiad Hoi/a carnosa it fre- 

 quently happens that two aerial roots of the same 

 stem may arise very close together and during growth 

 outside the mother-stem may become pressed and 

 flattened against each other along the greater part or 

 the whole of their length ; tangential and radial 

 divisions occur in the epidermal cells of the uniting 

 sides of each root forming a pseudo-parenchymatous 

 tissue common to the two roots. In a case like this 

 the union does not extend more deeply than the 

 cortex. In view of the crowded arrangement of the 

 roots of the ivy on many parts of the stem, union 

 between any two roots is not a surprising pheno- 

 menon. 



