1 64 THE ANATOMY OF WOODY PLANTS 



organization and separated from the fibrovascular category of tis- 

 sues by the endodermis. To the left in the figure the siphonostele is 

 depicted in a continuous or closed condition, while on the right it 

 is open on one side. The opening corresponds to the giving off 

 of the trace of an appendage, which in this instance is a leaf. A 

 general feature of the tubular or siphonostelic central cylinder in 



FIG. 119. Diagram of a siphonostelic stem 



the ferns and their immediate allies is the appearance of openings 

 in the tubular central cylinder which correspond to either leaves or 

 branches. These openings persist for a longer or shorter distance 

 above the point of departure of the fibrovascular supply to the 

 appendage and are known as leaf gaps or branch gaps according 

 to the organ involved. Around the edges of these gaps the endo- 

 dermis of the inside becomes continuous with that of the outside. 

 Usually, too, the phloem of the inner surface of the tubular stele 

 joins with that situated on the exterior. Naturally, also, the 

 fundamental tissue of the outside, commonly known as the cortex, 



