102 



BOTANY 



PART I 



division, and later undergoing as a rule transverse divisions. They are narrower 

 than the sieve-tubes themselves, and are further distinguished from them by their 

 abundant protoplasmic contents. In some cases laticiferous- or mucilage-tubes 

 occur in the phloem. 



The bundle as a whole is often more or less completely surrounded 

 by a BUNDLE SHEATH. This may have the form of parenchyma 

 without intercellular spaces, the cells often containing large starch grains 



Fio. 120 A. Transverse section of avascular bundle from the internodeof astemofZeaMais. a, Ring 

 of an annular tracheide ; sp, spiral tracheide ; m and m', vessels with bordered pits ; v, sieve- 

 tubes ; s, companion cells ; cpr, compressed protophloem ; I, intercellular passage ; rg, sheath ; 

 /, cell of fundamental tissue, (x 180. After STRASBURGER.) 



(STARCH SHEATH) ; in other cases it is sclerenchymatous, or it consists 

 of endodermal cells or of cutis tissue. It is not regarded as forming 

 part of the vascular bundle itself. The sheaths frequently serve to 

 limit the conduction of material to the vascular bundle. Sclerenchy- 

 matous sheaths are most common at the outer side of the phloem, 

 forming semilunar masses (Fig. 120 A, 121 vg\ and are especially 

 developed in relation to the outermost bundles when these have a 

 scattered arrangement. 



