6 
F. Cavers. 
above and below by the hyaline cells, and may be spindle-like in 
cross-section, their ends reaching neither the upper nor the lower 
side of the leaf. The classification of the Sphagna is largely based 
Fig. 59. Sphagnum acutifolium ; the upper figure shows a portion of a 
mature leaf in surface view, the lower a portion of a transverse section of 
the leaf. 
on the appearance of the two kinds of leaf-cells as seen in cross- 
section. 
The inner tissue of the main stem consists of long cells sharply 
separated from an outer zone of short cells (Fig. 57b, Fig. 60). The 
latter (cortex) is at first a single layer, and in the branches it 
usually remains one cell thick, but in the main stem it often 
becomes four layers deep, its cells being large and colourless in 
