190 



STEMS 



Fig. 168. — Lengthwise section through a vascular bundle of Com, the 

 knife sphtting the bundle as shown by the hne (o) in Figure 167, thus missing 

 the pitted vessels, x, 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 (e) and companion cells (c); 

 s, strengthening tissue. Highly magnified. 



FiQ. 169. — Vascular elements common among Ferns and Seed Plants, a, 

 spiral vessel; 6, annular vessel; c, pitted vessel; d, reticxilated vessel; e, sca- 

 lariform vessel; /, elements of the phloem showing sieve vessel with sieve 

 plate Ql), and companion cell (c). Highly magnified, a and b, after Bonnier 

 and Leclerc Du Sablon; c, after DeBary; d, modified from Barnes; e, modi- 

 fied from Cowles; and/, from Strasburger. 



