172 



Practical Plant Biology. 



vertical branches, or cones, are all similar in size and are distri- 

 buted uniformly round the stem. In the angles between the 

 leaves and the stem are seen minute whitish globular bodies which 

 are sporangia. 



In structure the small leaves resemble those of a fern rather 

 than those of a moss, with which we might at first be inclined to 

 compare them. They have a thick mid-rib, and on either side of 

 it the green tissue is several layers of cells thick and, as in the 

 fern, the mesophyll towards the under surface is more loose and 



FIG. 46. Selaginella, stem, transverse section, x 150, showing three con- 

 ducting tracts, each suspended in a tubular space. The axis of each 

 tract is occupied by a strand of wood. Outside this is the bast. (From 

 Evans' An Intermediate Textbook of Botany. After Sachs.) 



spongy than that above it. It is covered over on both sides by an 

 epidermis and this sheath of cells is perforated on its under side 

 by stomata. The outer walls of the epidermis are covered with 

 cuticle ; the remaining walls of the epidermis and of the mesophyll 

 are thin. In each cell of these tissues there are one or two large 

 chloroplasts, a state of things very unlike the other ferns and 

 strangely reminiscent of the Algae. 



The structure of the stem is peculiar. It is a shaft of funda- 

 mental tissue traversed lengthwise by a tubular passage and 

 covered over by the epidermis. Running down the tube is a 

 vascular tract slung in its axis by elongated cells which are con- 



