88 PRACTICAL BOTANY 



ARBOREOUS TYPE 



I. Note the following external characters of a twig 

 of Elm (Ulmus campestris) of the current year. It is 

 cylindrical, hirsute, green or brown according to age, the 

 latter colour being due to the formation of a superficial 

 layer of cork. Small brown excrescences are scattered 

 over its surface ; these are lenticels. The arrangement 

 of leaves is alternate and bilateral, phyllotaxis J, branch- 

 ing axillary : at the base of each leaf, note on either 

 side a small scar, where the stipule was inserted : the 

 stipules usually fall away soon after the buds open in 

 spring, but they may sometimes be found persistent for 

 a time on strong shoots. 



II. Cut thin transverse sections of a twig of the 

 current year ; mount in glycerine, and examine with a 

 low power. Other sections may, for comparison, be 

 treated with chlor-zinc-iodine, others again with acidu- 

 lated solution of aniline sulphate. 



Observe the general arrangement of tissues in con- 

 centric layers, which will be found to succeed one 

 another in the following order, starting from the 

 outside : 



1. Epidermis : a single layer of small cells: many 

 of them have grown out, as conical hairs, perpendicular 

 to the surface. 



2. Cork : consisting of one or more layers of square 



