458 OPHIOGLOSSALES 



downward one of reduction. Before discussing these two alternatives, it 

 will be necessary to look into the anatomy of these plants, since arguments 

 on that ground have been held to be very material to a decision. 



ANATOMY. 



The roots of the Ophioglossaceae show a wide range of internal 

 structure. 1 In Helminthostachys they are tetrarch to heptarch, and most 

 commonly hexarch, with central pith, alternating phloem, a large-celled 

 pericycle, and endodermis. In Botrychium the number of protoxylems 



FIG. 256. 



Ophioglossuin Bergianujn, Schlecht. Transverse sections of the stele of a root, the one 

 showing two unequal groups of xylem, the other only one. X 200. 



varies a good deal, common numbers being two and three, but it has 

 been shown in B. Lunaria that roots which are diarch distally may be 

 monarch near the base. In Ophioglossum, also, there is some variety, for 

 in O. pendulum diarch, triarch, and tetrarch roots have been described, 

 while in this species also a monarch structure has been seen at the base 

 of a rootlet : O. decipiens has triarch structure : O. 'palmatum is diarch. 

 Most of the species of Euophioglossum have monarch roots, and this is 

 conspicuously so in O. vulgatum. In O. Bergianum the structure may be 

 diarch or monarch, the latter having been observed in roots close to their 

 base (Fig. 256). With the monarch structure goes bifurcate branching, 

 while monopodial branching is seen where the structure is more complex, 

 as in O. pendulum, Helminthostachys, and Botrychium. Thus both dicho- 

 tomous and monopodial branching are found in the same genus. Possibly 

 dichotomy . is restricted to the monarch roots : this was suggested by Van 

 Tieghem, who remarks that, if the monarch root divides, we know 

 beforehand that it will dichotomise. 2 



It is the fashion of the time to hold that all monarch roots are 



1 Compare Boodle, Ann. of Bot., xiii., p. 377, where the literature is fully quoted. 

 "-Ann. Sci. Nat., V. Serie, T. xiii., p. 108. 



