STEM OF .ZEA MAIS. 



103 



now concerned were still in process of rapid elongation. Imping- 

 ing on the intercellular passage on its outer side are one or more 

 other vessels. They are recognisable by their cavity, which is 

 larger than that of the neighbouring cells. In the bundle repre- 

 sented in Fig. 40, only one such vessel (sp), and that a rather 

 narrow one, is present. These vessels, present to the number of 

 one or more, are, as can be demonstrated only in longitudinal 



FIG. 40. Cross-section through a vascular bundle from the inner part of the inter- 

 iiode of the stem of Xea Mais. , Segment of an annular vessel ; sp, spiral vessel ; 

 m and m', pitted ducts with uubordered pits ; v. sieve-tubes ; s, companion-cells ; 

 jrr, crushed elements of the protophloem : I, intercellular passage ; *x/, sheath ( x 180). 



section, thickened in a spiral manner. They are spiral vessels. 

 Next, in each half of the bundle, right and left, is a wide cavity 

 (m, m'). These are two vessels with pitted, rarely spirally reticu- 

 late, thickened walls. They are the so-called pitted ducts. Often 

 in the cavity of these great vessels a ring, or part of one (*') 

 can be seen projecting as a thickening of the wall. This is the 

 remains of a cross partition-wall which, diaphragm-like, is broken 



