29] 



CHAPTER II. THE TISSUES. 



105 



c. Groidng-points with a group of common initial cells occur in 

 certain Pteridophyta (e.g. in the stems and roots of Marattiacese, 

 of Osmunda sometimes ; stems of Lycopodium, Isoetes, some 

 Selaginellas). In these cases, there is a grcrap of frequently fovir 

 cells which are the common initials of the tissue-systems. The 

 general relations of the tissue-systems are here essentially the 



PIG. 86.-Median longitudinal section through the apex of the root of Pter'.t cretica ; t 

 apical cell; fc initial segment of dermatogen; fc, outermost layer of root-cap ; p wall mark- 

 ing limit between the plerome P and the periblem Pb ; c wall marking the inner limit of 

 the outer cortex. (After Strasburcrer : x 2 10.) 



same as in those forms in which the growing-point has a single 

 apical cell. 



The Growing-jjoint in the lower plants. In the gametophyte of the Bryo- 

 phyta, the growing-point of the stem or of the thallus has either a single 

 apical cell (all Mosses ; Jungermanniacese) or a group of apical cells 



