198 



THE STRUCTURE OF ECONOMIC PLANTS 



around the periphery of the leaf blade or base and are parallel 

 throughout its entire length. There are many small branches and 

 cross-connections between adjacent bundles which arise in the rows 

 of parenchymatous cells that surround and separate the bundles. 



_3>^.^-X--lac 



par 



=^ lac 



Fig. 91. A, diagrammatic transection of the lamina showing distribution of bundles and 

 large central lacuna; B, a section of A showing cellular detail : cti, cuticle; ep, epidermis; 

 /' sp, intercellular space; lac, lacuna (broken down parenchymatous cells are shown on the 

 margin of lacuna in B); pal, palisade cells; par, parenchyma; ph, phloem; sto, stoma; 

 xy, xylem. 



There are relatively few transverse veinlets in the lower half of the 

 outer sheaths of the mature bulb, but many occur in the upper parts. 

 The unthickened sheaths of a young onion have numerous cross- 

 connections at all levels. Both large and small bundles may origi- 

 nate blindly and then anastomose with larger ones, while some of the 



