196 BOTANY. 
dying at the end of each year: these are called the annual 
stemmed species. In other species the aerial stems also 
persist; the latter are hence known as perennial-stemmed. 
411. The epidermal cells i 
are mostly narrow and elon- 
gated. The breathing-pores, 
which are present in all the 
chlorophyll-bearing parts of 
the plant, are arranged with 
more or less regularity in 
longitudinal rows; on the 
stem they occur in the chan- 
nels between the numerous 
ridges. 
Fie. 108. Fig. 109. 
Fic. 108.—Part of a green stem of the Great Horsetail (Equisetum telmateia), 
showing its structure; “and a whorl of united leaves, with part of a whorl of 
gna oy pate: izes re 
ria .—A, part of an old cone of the Great Horsetail, showing three sepa- 
rated whorls of shield-shaped leaves; B, three shield-shaped flew yen: slightly 
magnified; st, stalk, and s, expanded part of leaf; sg, the spore-cases, 
412. The fibro-vascular bundles of the stem are disposed 
in a circle, and run parallel with each other from node to 
