568 A TEXTBOOK OF THEORETICAL BOTANY 



The cones are borne at the apices of the upright branches, and below 

 each cone the branch elongates into a portion sparsely covered with leaves. 

 The cones themselves are made up of closely set, acutely pointed leaves, 

 which are termed sporophylls, and in the space between each sporophyll 

 and the axis of the cone, a single kidney-shaped sporangium is produced. 



Fig. 576. — Lycopodhim clavotuvi. Fertile plant 

 bearing strobili. Half natural size. 



Anatomy of the Stem 



The stem anatomy is complex though not so elaborate as that of the 

 Ferns. There is no true apical cell, but there is a rounded group of initial 

 cells. Branching is quite independent of leaf formation, the branch rudi- 

 ments appearing on the dorsal side of the growing point. Branching is thus 

 monopodial (see p. 838) and the stem is dorsiventral. In the mature stem 

 there is a broad cortex separated from the central stele by a pericycle 

 consisting of several layers of thin-walled cells (Fig. 577). 



There is no endodermis present. The cortex has three zones. There 

 are peripheral and central zones of thickened sclerotic cells and a middle 

 zone in which the cells are larger and thin-walled, containing a few chloro- 

 plasts. The single stele occupies about half the area of the section. It 

 consists of a number of irregularly shaped, parallel plates of xylem alternating 

 with bands of phloem. The xylem is composed predominantly of scalariform 

 tracheids, with no vessels and no parenchymatous cells. Each xylem plate 

 is surrounded by a single layer of parenchyma, with bordered pits on the 

 inner walls, which lies between the xylem and the phloem. The phloem 

 consists of sieve tubes and parenchyma only. The development of both the 



