Lecture XXV. 223 



and from the conducting tracts of the stem branches are given off 

 to supply them. As these branches pass out they undergo a twist 

 and at the same time converge together. The protoxylem, which' 

 is innermost in the stem, passes to the outside of the wood in the 

 root, while the filaments of primary wood drawing together occupy 

 the axis of the root. In this way a core of primary wood forms 

 the axis of the root, while three, four or five ridges of protoxylem 

 run along its surface. In each groove, between the ridges of protoxy- 

 lem, lies a strand of bast. A layer of cells the pericycle covers 

 this cylinder of conducting tissue and over all is a thick coating of 

 cortex. The innermost layer of the cortex limits the conducting 



FIG. 77. Ranunculus repens, root transverse section, x 50. 

 6, conducting tract ; c, cortex. 



tract and is known as the endodermis. The outermost layer pro- 

 duces elongate tubular cells projecting from its surface the root- 

 hairs. A root-cap is formed covering thegrowing tip of the root 

 and facilitating the passage of the root among the soil particles by 

 the exuviation of its outer dead cells. 



From the description just given of the anatomy of the Buttercup 

 it will be evident that the conducting tracts, or vascular bundles, 

 are the channels of transport putting the absorbing surfaces of 

 the root into communication with the photosynthetic leaves. 

 The water entering at the root-hairs carries with it various 

 nutritive substances in solution, derived from the soil, and is 



