166 PRACTICAL BOTANY. 



near to the ends of the spindle-like vascular bundle ; 

 these are bundles of the leaf-trace cut through on their 

 course in wards from the leaves. Thus the whole bundle - 

 system of this shoot consists of a single central bundle, 

 which traverses the axis longitudinally, and gives off 

 smaller branch bundles, which pass outwards into the 

 leaves, one of them entering each leaf. 



The vascular system of the shoot is more complicated in certain 

 other species of Selaginella ; thus in S. Willdonovii, 8. incequa- 

 lifolia, &c., three large flattened bundles are seen in each 

 transverse section of the axis ; the planes in which these bundles 

 are flattened are parallel to one another ; in these species the 

 bundles may individually show considerable irregularities of out- 

 line : the whole arrangement of their vascular system may with 

 advantage be compared with that in the stem of Lycopodium. 



Note with a higher power : 



1. The general appearance of the Phloem, with its 

 highly refractive cellulose walls, and scanty protoplasm. 



2. Between this and the xylem a somewhat irregular 

 series of cells of the Conjunctive parenchyma, 1 with 

 thin cellulose walls and plentiful protoplasm. 



3. The chief constituents of the Xylem, viz., large 

 prismatic Tracheides, with peculiarly marked, lignified 

 walls. 



4. At the poles of the spindle-shaped xylem note 

 tracheides of smaller size ; these compose the first 

 formed Protoxylem : development thus proceeds from 

 the periphery to the centre. 



1 It has been suggested by Treub that this term, which has been 

 applied to the central parenchyma of certain roots, may be extended so 

 as to include that parenchymatous tissue which has been termed by 

 Russow "Geleitzelleo." 



