22 



Elementary Botany 



parts of plants, and contain nutritiye materials necessary for 

 the nourishment of the plant. When the disappearance of the 

 separating walls is more complete, so that the cells form more 

 or less long tubes, true vessels are produced, and these are 

 known, according to the nature of their component cells, as 

 pitted, spiral, annular, reticulate, or scalariform vessels. 



These true vessels usually possess a considerable quantity 

 of secondary deposit, and are seldom branched. As a rule 



Fig. 38. — Fusiform 

 bast fibre of the 

 Larch. 



Fig. 39. — Vesicular vessel in longitudinal section of 

 scaleof bulb of Onion(.^///K;« Cepd)\ e, epider- 

 mis with cuticle (c) ; p, parenchyma ; Sff, coagu- 

 lated contents contracted to show the porous 

 walls. (After Sachs.) 



they contain nothing but air ; but in the early spring, when 

 the stem is gorged with sap, they are often partly filled with 

 liquid. 



Bast tubes or bast fibres are generally more pointed and 

 sometimes branching (fig. 25). The coalescence between the 

 component parts is so complete that the separate cells cannot 

 be distinguished when the fibres are examined by means of the 

 microscope. Bast fibres do not often communicate directly 



