BOTANY. 



the bundles are curiously isolated from the surrounding 

 ground tissues of the stem. 



141. The bundle of the nearly related Lycopodium com- 

 planatum is much more complex in its structure (Fig. 101). 

 Here there are four parallel plates of tracheary tissue, each 

 having a structure like the single plate of the bundle of 

 Selaginella incequifolia. Between the tracheary plates there 

 is in each case a row of sieve tubes imbedded in a lignified 

 tissue composed of elongated cells (sclerenchyma, or fibrous 



Fig. 101. Cross-section of the stem of Lycopodium complanntum. The fibro-vas- 

 cular bundle is composed of four plates of tracheary tissue (darker in the figure), 

 between which are masses of lignifled tissue composed of elongated cells ; each of 

 these latter masses encloses a row of sieve tubes (larger and thicker walled in the 

 figure) ; the bundle sheath is seen to bound on its inner side a thick mass of very thick 

 walled fibrous tissue ; exterior to this (toward fi) is a layer of chlorophyll-bearing 

 parenchyma, bounded by a well-developed epidermis. The small vessels at the ex- 

 treme e'dges of the plates of tracheary tissue are narrow and spirally marked ; the 

 remainder of each plate is composed of scalariform vessels, x 100. After Sachs. 



tissue?). Around this central fibro-vascular portion there is 

 a layer of parenchyma, and outside of this a bundle sheath, 

 which is commonly regarded as marking the boundary of 

 the bundle ; it is doubtful, however, whether it should be so 

 considered, as exterior to it lies a thick mass of fibrous tissue 

 which completely envelops all the previously described 

 tissues.* 



* Sachs ("Text-Boot," p. 418) regards the stem of Lycopodium as 

 composed of four united bundles and compares them to the separate 

 bundles of Selaginella. De Bary ("Anatomic," etc., p. 363), on the 



