254 



STRUCTURAL BOTANY 



scale-leaf, as it protects the young organs of the bud 

 from the risk of drying up. 



c. Root 



The root-system of the Fir, and of Conifers 

 in general, consists of the main tap-root and its 



FIG. 104. Transverse section of the root of Picea excelsa at 

 the commencement of secondary thickening, px, px, the 

 two protoxylem groups ; uniting them is the primary 

 xylem-plate. Outside each protoxylem group is a resiu 

 canal. x 2 , first layers of secondary xylem ; c, cambium ; 

 ph, phloem; p.c, pericycle ; pd, periderm ; en, endo- 

 dermis. Outside this is cortex. Magnified 33. (R. S.) 



branches. Adventitious roots hardly ever occur in 

 these plants, unless it be on the base of the hypo- 

 cotyl, where they scarcely differ from the ordinary 

 rootlets. 



The general structure of the root is of the dicoty- 

 ledonous type that is to say, we find as a rule a 



