108 



PLANT STUDIES 



e p p/ p e 



cesses of the lower groups that it is regarded as the only 

 true root. It is quite uniform in sti'ucture, consisting of a 

 tough and iibrous central axis surrounded by a region of 

 more spongy structure. The tough axis is mostly made 

 up of vessels, so called l)ec;iuse ihcy 

 conduct nuiterial. and is called tlie 

 vascular axis. The outer more sjHUigy 

 region is the cortex, ivliich covers 

 the vascular axis like a thick skin 

 (see Fig. 10.5). 



<Jne of the peculiarities of tlie 

 root, in whicli it ditt'crs from tlu^ 

 stem, is tlnit the l)ra,nches come from 

 tlie vascuhir axis and hurrow thi'(Uigli 

 the cortex, so that "wlien tlic latter 

 is peeled olf the hi'a.nches are left 

 attached Ui the axis, and the cdi-tex 

 shows the holes through whidi they 

 passed. It is evident that when sudi 

 a root is ahsorhiiig. the alisorhcd nui- 

 terial (water with various materials 

 ill solution) is received into the 

 cortex, through whidi it must ]>ass 

 pears in the older parts of to the vascular axis to lie Conducted 



the root, and the pronii- / . i.i j. 



nent ront-r.ip ir). '^" ^^^^ Stem. 



Another ])e('uliarity of the root 

 is tlia.t it elongales only hy growth at the tip. while the 

 stem usually continues to elongate some distance hdiiiid 

 its growing tiji. In the soil this delicate growing tiji is 

 protected liy a little cap of cells, known as the rwi-cap 

 (see Fig. 105). 



Fig. 10.5. A loiiyitudiii 

 section through tile rtji 

 tip of shepherd's purs 

 eho\^■ing the central va 

 cnlaraxisC;? ), snrroundt 

 hy the cortex (/;), outsii 

 of the cortex tlie e] 

 dermis ie) which disaj 



