112 BOTANY. 



the bundles are curiously isolated from the surrounding 

 ground tissues of the steni. 



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 incBquifolia. Between the tracheary plates there 

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

 tissue composed of elongated cells (sclerenchynia, or fibrous 



Fig. 101.— Cross-section of the stem of I/ycopodium complanntum. The flbro-vas- 

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

 between which are masses of lignified 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 B) is a layer of chlorophyll-bearing 

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

 treme edges of the plates of tracheai-y 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 tlie previously described 

 tissues.* 



* Sachs (" Tert-Boot," p. 418) re^rds the stem of Lycopodium as 

 composed of four united bundles and compares them to the separate 

 bundles of Selaginella. De Bary ("Anatomie," etc., p. 362), on the 



