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 (Tilia) 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. 
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