ORIGIN OF ROOT 



22 



interest in any discussion of the origin of a subterranean absorptive 

 system. 1 



But the presence of such " rhizophores " does not greatly assist the 

 solution of the problem of origin of the roots themselves. There is, in 

 fact, no sufficient or decisive evidence how the root came into existence 

 in Vascular Plants ; but on the facts as they stand two alternative opinions 

 are possible. Either that it resulted from the transformation of a leafy 

 shoot by loss of the appendages, followed by other special adaptations in 

 relation to its life, and to its absorptive function in the soil. Or that it 





Fie. 113. 



Plant of Stlagiitella spinulosa, with root system springing from swollen knot at base of 

 the upright hypocotyl. i^ natural size. 



arose as a new type of haustorial outgrowth, not originally of shoot-nature ; 

 but nevertheless that in its first and less differentiated condition it 

 resembled the shoot from which it arose, in its structure, and in the 

 character of its branching. That those features which were helpful in its 

 absorptive and conducting functions were permanently maintained, and 

 they became distinctive characters of the differentiated root : other charac- 

 ters, such as the root-cap and endogenous branching, may have been added 

 in accordance with the underground habit. This latter view seems to me 

 the more probable alternative. 



Applying it in the case of the Lycopodiales, the root at its inception 

 would, like the stem of these plants, be exogenous, with exarch xylem 

 1 Compare Goebel, Organography, vol. ii., p. 230. 



