70 GROUPS OF TISSUES, OR TISSUE SYSTEMS 



types of glands may be found on the "tentacles" of the 

 leaves of the sun-dew (Drosera). 



(i) Section a very young twig of basswood (TiUa) or elm or 

 other tree and note the epidermis. Compare this with a one 

 or two year old twig of the same tree and note the cork forma- 

 tion. Study cross-sections of various kinds of tree trunks and 

 note the different types of cork formation in these. 



(j) On a young twig of elder (Sambucus), snowball (Vibur- 

 num) or birch (Betula) section the lenticels in different stages 

 of development and study them. 



(k) In the autumn make longitudinal sections through the 

 base of the petiole of leaves of maple, elm or other deciduous- 

 leaved trees. If made at the proper place and time the cork- 

 like abscission layer may be found. 



REFERENCE BOOKS 

 The books enumerated for Chapters I and II. 



