31.] 



CHAPTER II. THE TISSUES. 



153 



steles may remain distinct in the internodes, or they may fuse 

 more or less (Fig. 116 C). 



The general morphology of the tissues of the leaf is essentially 

 the same as that of the stem which bears it. When the stem is 

 polystelic, one or more complete steles enter the petiole of the leaf 

 which is, consequently, either monostelic or polystelic. When 

 the stem is monostelic, each leaf receives a portion, termed a 

 meristele, of the stele of the stem ; this meristele may be either 

 entire, or be split up into a number of schizosteles, each of which 

 may consist of but little more than a vascular bundle. 



--find. 



-End. 



FIG. 116 Portions of transverse sections of stems of species of Equisetum, illustrating 

 scliizostely (after Pfitzer: x 36). B Typical Bchizostelic rhizome of E. litorale; C 

 schizostelic gamodesmic rhizome of E. silvaticum ; A aerial stem of E. palustre, in which the 

 structure is che same as in C, but the markings of the internal endodermal layer are not 

 developed, so that the stem appears to be monostelic; a central cavity; b vallecular 

 cavities in the cortex ; c carinal cavities in the schizosteles ; End. endodermis. 



The primary tissues that is, the tissues which are developed 

 from the primary meristem of a growing-point or of an embryo 

 will now be considered in detail. The following account, unless it 

 is expressly stated otherwise, refers exclusively to the sporophyte 

 of the Vascular Plants. 



31. The Primary Tegumentary Tissue. The primary 

 tegumentary tissue may be generally described as the external 



