GLOSSARY. 55 



cortex. This sheath is chiefly concerned in supplying the leaves with their 



first vascular bundles, and is the centripetal vascular cylinder of many 



Carboniferous stems. 

 Meristem. — Cells capable of multiplication by the formation of septa or walls 



crossing their inner cavities. 

 Monarch, Diarch, &c. — In a transverse section of a young root, the first-formed 



vessels appear at a variable number of points near the circumference of a 



central cellular cylinder. The vascular bundles of roots are called Monarch 



when there is but one such initial point. Diarch if two. Triarch if three, &c. 

 MoxoromAL or false Dichotomy. — Where the apex of a growing shoot advances 



whilst any lateral branches, however near to the apex, arise from a place 



lower down than the true apex. 

 Orientation. — The uprising of branches from some other organ, as of foliar 



bundles from the centripetal cylinder of a Lepidodendron or of rootlet bundles 



from the exogenous zone of Stigmaria. 1 

 Parenchyma. — Cells whose length does not greatly exceed their breadth. 

 Periderm. — An external protective layer of the bark replacing the detached 



epiderm of young plants. It is usually a Phellem, i. e. cork. 

 Phellem. — A peripheral cork-layer of the bark developed centripetally from the 



exterior of the Phellogen. 

 Phellodeiim. — A cellular layer of the bark developed centrifugally from the inner 



side of the Phellogen. 

 Phellogen. — A thin meristem cambium-layer in the cortex. 

 Phloem. — The bast portion of a fibro-vascular bundle characterised by the 



presence in it of sieve-tubes or their representatives, as the xylem or wood 



portion is characterised by the presence of vessels or Tracheids. 

 Phyllome. — A modified part of a plant primarily capable of developing into a leaf, 



e. g. each of the parts of a flower. 

 Prosenchyma. — Elongated, spindle-shaped cells with pointed or oblique ends. 

 Proximal. — The end of an organ nearest to the centre of the organism to which 



it is attached. 

 Quincuncial. — A term applied to the arrangement of the rootlet-scars of Stig- 

 maria, each one of which occupies the centre of a surrounding group of four 



similar ones. 

 Rhizome. — A creeping subterranean stem, capable of giving off leaves or aerial 



shoots from its upper surface and from the ends of its branches, and roots 



from its lower surface. 

 Root. — A descending axis in contra-distinction from a stem or ascending axis. 



1 This definition of " Orientation " represents the meaning of the word as used in the Monograph, 

 but differs from that assigned to it by the French botanists. 



