374 



MANUAL OP BOTANY 



remain fused in front and behind them, giving the appearance 

 of an internal and external shoath {fig. 151, b). In some cases 

 the inner endodermis is almost or entirely indistinguishable, 

 when the structure simulates a monostele. The separate bundles 

 of the Equisetums are peculiar in having a large lacunar space 



Fie. 761. 



Fig. 761. Gamoatelic stem of Marsilea. cp. Epiclerniis. co.la. Cortical 

 laounie. scl. Solerenchyma in tlie cortex. e«,. Outer; en^. inner fused 

 eudodermls of the steles. The steles are fused together laterally, forming 

 a TascuL^r ring in the centre of the stem surrounding a small portion of 

 the ground tissue. ' 



in the region of the xylem, causing the latter to be represented 

 by only a few vascular elements (fig. 758). 



The bundles in schizostelic stems are always collateral. 



Polystelic Stems.— In these as in the last described type the 

 first-formed stem is monostehc, but as it grows the differentia- 

 tion of the tissue of the pleronie becomes irregular, giving rise 

 to several steles separated by conjunctive tissue (fig. 760). Each 



