SELAGINELLA SPOROPHYTE 153 



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. 

 Note with a higher power 



1. The general* appearance ot the phloem, with its highly 

 refractive cellulose walls, and scanty protoplasm. 



2. Between this and the xylem is a somewhat irregular series 

 of cells of the conjunctive parenchyma, with thin cellulose walls 

 and plentiful protoplasm. 



3. The chief constituents of the xylem are 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 : 

 the development of the xylem thus starts from the periphery 

 and proceeds towards the centre of the oval xylem. 



IV. Cut transverse sections of fresh leaves held in a piece of 

 pith : mount in water or weak glycerine, and observe 



1. The epidermis of the upper surface consists of conical 

 cells, each of which contains a single large chlorophyll corpuscle. 

 Stomata are absent. 



2. Beneath this is the spongy parenchyma, which incloses 

 centrally 



3. A single vascular bundle. 



4. The epidermis of the lower surface consists of smaller cells 

 containing chlorophyll, and with stomata opposite the midrib. 



V. Cut longitudinal sections through fertile branches similar 

 to those cut from the vegetative bud, and examine them under a 

 low power. In the lower part, if the section was median, the 

 same succession of tissues may be recognised, as has been 

 already described in the transverse section (III.) Starting 

 from the outside, they will be as follows : 



1. Epidermis } these are hardly to be distinguished one 



2. Outer cortex J from another : the cells of both are pros- 

 enchymatous, and thick-walled, and show a gradual transition 

 to 



3. The inner cortex, in which the walls are thinner, and 

 the form of the cells parenchymatous. 



