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Fic. 168. — Lengthwise section through a vascular bundle of Corn, the 
knife splitting the bundle as shown by the line (0) in Figure 167, thus missing 
the pitted vessels. 2x, xylem showing spiral vessel (h) and annular vessels 
(a) which have been so torn by the growth of the stem that only the rings 
are left; p, phloem consisting of sieve vessels (¢) and companion cells (c); 
s, strengthening tissue. Highly magnified. 
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Fia. 169. — Vascular elements common among Ferns and Seed Plants. a, 
spiral vessel; b, annular vessel; c, pitted vessel; d, reticulated vessel; ¢, sca- 
lariform vessel; f, elements of the phloem showing sieve vessel with sieve 
plate (h), and companion cell (c). Highly magnified. a and b, after Bonnier 
and Leclerc Du Sablon; c¢, after De Bary; d, modified from Barnes; ¢, modi- 
fied from Cowles; and f, from Strasburger. 
