«■ 



ISOETES JAPONICA, A. BR. 



357 



Eoots from tlie two arms of the rhizophore-stele are arranged on the right and left 

 halves of each lobe of the caiidex respectively (text-figs. 15, 17). 



In general, the arrangement of the roots on the flanks of the two stelar arms 



is essentially the same as in the tri-lobed species (compare text-figs. 15, 16, 17 with 

 text-figs. 9, 10, 11 ; also cf. Stokey, 32, PL 19. fig. 6 *) ; further description is therefore 



unnecessary. 



r 



Before leaving the subject of the root-arrangement in Isoetes, a very simple method 

 of calculating the approximate total number of roots produced by any given plant may 

 be mentioned. In text-figs. 11, 14, 15, 18, it will be noticed that the number of 

 roots produced in any series always corresponds to the number of that series, e. g., in 

 series 1 there is one root, in series 2 there are two roots, in series 3 three roots, and so 



forth . 



Text-% 15 



Zl 



zi 



Z29 



Isoetes Jaciistris. Diagram showing arrangement of the roots on one half of the rhizophore-stele 



i 



numbers correspond with those of text-figs. 16 and 17. 



The 



Text-fig. 16. 



Isoetes lacustris. Diagram showing the arrangement 



of the first seven roots of a young plant. 



Text-fig. 17. 



/H- It 2.1 22 



"f 



IS- 



Isoetes lacustris.- Diagram showing order in which the 

 roots are differentiated. From a transverse section 

 of the caudex. 



* Stokey (l. c. p. 31 5), however, states that "the youngest sets of roots are those nearest the furrow ; and of those 

 in the furrow the youngest are at the ends." This statement is incorrect, because all the roots belonging to any 

 series are of the same age (see text-%. 18). 



