190 



STEMS 



FIG. 168. Lengthwise section through a vascular bundle of Corn, the 

 knife splitting the bundle as shown by the line (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. 



b c 



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

 spiral vessel; b, annular vessel; c, pitted vessel; d, reticulated vessel; e, sca- 

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

 plate (/O, and companion cell (c). Highly magnified, a and 6, after Bonnier 

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

 fied from Cowles; and/, from Strasburger. 



