THE ROOT. 



71 



Congenital. 



Franke made an interesting observation of this type 

 of union with regard to the aerial roots of the 

 Virginian trumpet-flower {Tecoma radicans), and also 

 in the roots of Rhus radicans. The roots occur in 

 rows of four or five. There is at first a common 

 rhizogenous meristem out of which the separate root- 

 apices become differentiated, and these form the 

 common dermatogen- and periblem-tissues of the 

 compound root. 



There is thus a congenital union of the dermatogen 

 to form a common root-cap and a similar union of the 

 periblem to form a common cortex; there are, however, 



Fig. 20. — Rhus radicans. Three congenitally-fused rootlets with the 

 plerome of each distinct. (After Franke.) S, tissue of mother- 

 stem, pi, plerome. pb, periblem. dm, dermatogen. 



three distinct plerome-tissues giving rise to three 

 separate vascular cylinders. The presence of separate 

 apical meristems and of separate vascular cylinders is 

 an indication that we are here dealing with a congenital 

 fusion of distinct roots (fig. 20). 



On becoming freed from the mother-stem the indi- 

 vidual roots tend to separate mechanically, each growing 

 thereafter greatly in length. Fermond seems to have 

 observed a similar phenomenon in the willow (Salix), 

 where three rootlets were seen to emerge from the 

 same lenticel on the parent-root ; they were congenitally 

 fused. 



Conclusions. — The abnormal cases of root-branch- 

 ing above described are obviously all due to hyper- 



