§30 



A TEXTBOOK OF THEORETICAL BOTANY 



in the embryonic foot which attaches the young sporophyte to the gameto- 

 phyte. This foot, not the primary root, is the true anti-apex of the embryo 

 in such types. In the embryonic Lycopod the first root is normally a side 

 growth, sometimes indeed arising close to or even actually at the stem apex. 

 The anti-apical position of the primary root with which we are familiar in 

 the Dicotyledons has only been reached in the higher plants in association 

 with the enclosed embryo and the disappearance of the attaching foot. 



Bower has called the young stages in the development of the Bryophyte 

 embryo the " primitive spindle," the anti-apex of which is also a foot, not a 

 root. The view here put forward is therefore in sharp contrast to that of 

 Campbell, who traces the origin of the root to the meristematic base of the 

 sporophyte in Anthoceros, on the assumption that the primary root is itself 

 the anti-apex. 



It seems much more probable that root and shoot have both alike been 



O 



THALLOPHYTE 

 STAGES 



Fig. 829.- 



^HOLDFAST 



^9 



PSILOTUM 

 STAGE 



-PRIMARY 

 ROOT 



FERN BOTRYCHIUM SPERMATOPHYTE 

 STAGE STAGE STAGE 



-Diagram to illustrate the theory that root and shoot are tsvo differentiated 

 positions of a primitive dichotomous thallus. 



differentiated from the branches of a dichotomous body like the rhizome of 

 Psilotiim. The close resemblance of this rhizome to the prothallus stamps 

 it as essentially primitive, though it already shows a differentiation into 

 branches which produce leafy shoots, and branches which remain under- 

 ground, a mode of differentiation which strongly suggests the origin of the 

 root system from specialized branches of a rhizome (Fig. 829). If this be so 

 we would conclude that a condition in which there are many lateral roots is 

 more primitive than one in which there is a single, anti-apical root. It is 

 interesting therefore to note that von Goebel maintains, on different grounds, 

 the same position. He calls the Pteridophyte type, which lacks an anti- 

 apical root, homorhizal, and the more advanced type, with opposed root 

 and shoot poles, allorhizal. To arrive at the latter condition the many 

 dichotomies of the rhizome, such as that of Psilotum, have apparently been 

 reduced to one, occurring in the early divisions of the embryo. The divergence 

 to the extreme of 180 of the two axial poles thus produced may be put down 

 to the advantages secured by this divergence, in view of their opposed 

 biological functions (see Fig. 628, d). 



