HISTOLOGY OF ANGIOSPERM STEM, ROOT, ETC. 103 



113. Apical Meristem of Bud of Lilac. Remove the 

 outer scales and leaves from a resting (winter) bud, then cut longi- 

 tudinal sections, cutting in a plane joining two opposite rows of 

 leaves. Clear the sections with potash or eau de Javelle. 



Note the broad rounded apex, with the young leaves in various 

 stages of development, the dermatogen, the procambial strands, 

 and the ground meristem. In some of the sections may be seen the 

 first spiral vessels of a vascular bundle. 



Cut a series of transverse sections and compare them with the 

 longitudinal sections. 



114. General Structure of Woody Stem. From 

 twigs of Sycamore, Horse Chestnut, Elder, Lime, Willow, 

 Apple, and other woody plants, peel off (1) the cork, and 

 note (2) the green cortex, (3) the phloem, a zone of 

 colourless tissue separated by (4) the thin sticky cambium 

 layer from (5) the hard wood, (6) the central pith. Note 

 that the surface-markings of the twig include (1) leaf- 

 scars, where the leaves of former seasons fell off ; 



(2) girdle-scars zones of closely-set scars, where the 

 scales fell from the opening buds of previous years ; 



(3) leuticels usually raised patches differing from the 

 rest of the cork in colour and texture. 



Note that the lenticels are not merely surface markings 

 or projections, but that each lenticel goes right through 

 the cork this is easily seen on stripping off, layer after 

 layer, the white papery bark of a Birch, in which the 

 dark transversely- elongated lenticels are very conspicuous. 

 A lenticel is a local modification of the cork a place 

 where, instead of compact impervious cork, there has been 

 produced loose powdery tissue through which gases can 

 pass into and out of the living tissues within the cork 

 ( 115, 123). 



115. Experiments with Lenticels. (1) Dip a twig 

 of Elder, or other plant with conspicuous lenticels, into 

 boiling water; air-bubbles escape from the lenticels. 

 (2) Fix one end of a cut twig (about 10 cm. long) of 

 Elder, etc., on to the nozzle of a bicycle pump by means 

 of stout rubber tubing ; seal the free end of the twig by 

 tying on a piece of rubber tubing, folding it, and again tying 

 it to the twig. Put the whole into a jar of cold water, so 



