the Periderm of Fossil Lycopodiales . 3 1 1 
thin-walled and often crushed and distorted (Text-fig. 23, a), or with the 
walls broken down so as to produce a series of holes (Text-fig. 23, b). 
Sometimes one or two of the cells show signs of tangential division. In 
many sections the zones appear merely as broken, narrow, black bands. 
In Lepidodendron Wunschianum the zones are much more continuous, 
A 
B 
Text-fig. 24. Lepidodendron Wunschianum. Zones in the periderm. A, transverse section. 
c , crack. Will. Coll., 452. B, radial section. Will. Coll., 446. x 265. 
* 
and, owing to the lightness of colour of the cells and their thinner walls, 
they stand out as concentric white lines in the periderm. Many of the cells 
appear to have undergone recent division, and some are disorganized or, as 
is much of the periderm, masked by dark substance (Text-fig. 24). These 
