THE TISSUE SYSTEMS 9 



transverse section of the creeping stem of Pteris aquilina. Through- 

 out the area of the figure are scattered oval masses, the fibro vas- 

 cular bundles. These are very sharply marked off from the rest 

 of the tissues by a boundary appearing as a dark circumscribing 

 line. On the outside of the stem is the integumentary system, or 



FIG. 6. Transverse section of the rootstock of Pteris aquilina, showing three 

 categories of tissue namely, epidermal (external), vascular, and fundamental. 



epidermal tissue, consisting of a single layer of cells. The epidermis 

 is characteristically uniseriate in the lower forms, and only in some 

 of the higher vascular plants does it become a multiple layer. The 

 remaining structures of the stem of the bracken fern belong to the 

 fundamental system. The next illustration (Fig. 7) shows a part 

 of the stem of Pteris more highly magnified, so that the details of 



