CONIFERALES 



269 



are either plerome or give rise to it. However, just how definite the 

 differentiation into periblem and plerome may be within the meriste- 

 matic group is not so easy to determine. There is certainly no such 

 marked differentiation as in the Capsella type among dicotyls. 



It was once claimed that there is no true epidermis in Pterido- 

 phytes except at the root cap, because it was only at this point that 



Fig. 275. — Taxodiitm imbricariuni: extreme swelling of the lower part of the tnmk. 

 The swollen part of the tree at the right is covered with adventitious roots. After 

 KuRZ.333 



there was a segment of the apical cell giving rise to the special layer. 

 As a matter of fact, the layer which was called periblem was still an 

 embryonic layer which had not yet become differentiated into peri- 

 blem and dermatogen. No doubt, conifers have an epidermis. 

 Whether it is better to say that the epidermis comes from the peri- 

 blem, or that an embryonic region is late in differentiating into peri- 

 blem and dermatogen, may be a problem which different people 

 will decide differently. At any rate, the group of initials, as one sees 



