222 PLANT MORPHOLOGY 



The stele is enclosed by a parenchymatous pericycle, one or more layers 

 of cells in thickness, outside of which is an ill-defined endodermis, consist- 

 ing of a layer of cells with cutinized walls (Fig. 176). As in all vascular 

 plants, the conducting system is essentially continuous throughout the 

 plant body. From the stele of the stem a strand of conducting tissue, 

 called a leaf trace, extends through the cortex to enter each leaf and 



Fig. 178. Cross section of the central portion of the stem of Lycopudium compla/iattirn, 

 showing the "parallel-banded" type of stele, X 130. 



become its vein. Similarly each branch is connected with the stele of the 

 main stem by a branch trace and each root by a root trace. These traces 

 are present in all vascular plants. 



Like the stem, the root of Lycopodinm is an exarch protostele, but 

 nearly always shows the radial arrangement of xylem and phloem, even 

 where the stem is of the mixed or parallel-banded type. The striking 

 similarity between the root and stem of Lijcopodium bespeaks a very 

 ancient origin for the genus, for in the higher groups of vascular plants the 

 organization of the stem becomes increasingly more advanced, while that 

 of the root remains unchanged. 



The vascular system of Phylloglossum is poorly developed and shows 

 evidences of reduction. The tuber consists mainly of compact storage 



