60 PRACTICAL BOTANY 



the whole radial surface : it is therefore better not to attempt 

 it, but to study the several structures in a number of succes- 

 sive sections, each extending over only a part of the radial 

 surface. 



Starting from the outside, observe the same succession of 

 tissues as already seen in the transverse sections, viz. : 



1. Epidermis, which is often dried up and disorganized. 



2. Cork (including the cork-cambium and phelloderm), with 

 the short cells arranged in radial rows. 



3. Cortical tissue, with large mucilage cells. 



4. Hard bast, consisting of long fibres. 



5. Soft bast, thin- walled elements with much protoplasm. 



6. Cambium, a misty band ; cells not easily defined. 



7. Xylem, with thick lignified walls, the vessels appearing as 

 large tubular cavities. 



8. Pith, parenchymatous ; its appearance as in transverse 

 sections. 



Note the medullary rays, which appear as narrow bands of 

 parenchyma, following the plane of section. 



Examine these several tissues in detail with a high power. 



1. The epidermis, when still persistent, shows the same 

 characters as are observed in transverse sections. 



2. The cork is composed of square cells arranged in radial 

 rows, which are continuous through the cork-cambium to the 

 phelloderm, the latter presenting much the same appearance as 

 in transverse section. 



3. The cortical tissue, which is parenchymatous throughout, 

 also appears much the same as in transverse section. 



4. The hard bast consists of long fibres, with thick walls, 

 and very small cell-cavity : they are distributed in irregular 

 groups among 



5. The soft bast, which is characterized by thin walls and 

 protoplasmic contents, and is composed of 



a. Sieve-tubes, which are best seen in the part of the phloem 

 nearest to the cambium : the sieve-plates are oblique, and face 

 the radial planes. The sieve-tubes may easily be recognized in 

 stems cut in autumn by the masses of callus which surround 

 the sieve-plates : this stains brown with chlor-zinc-iodine. 



