42 PRACTICAL BOTANY 



sections, and compare those results with the observations about 

 to be made. 



Starting as before from the periphery, note successively the 

 tissues already observed in the transverse sections. It is but 

 rarely possible to see all the tissues satisfactorily represented in 

 a single radial section, therefore the study of the tissues and 

 of their relative positions should be conducted by comparison 

 of a number of sections one with another. 



1. The epidermis, consisting of oblong cells, whose walls and 

 contents present the appearance already observed in the 

 transverse sections. Note the disturbance of their normal 

 arrangement around the bases of the larger hairs. 



2. Beneath the epidermis lies the collenchyma, consisting of 

 oblong cells with thick longitudinal cellulose walls (blue, chlor- 

 zinc-iodine), and thin transverse ends : the contents are proto- 

 plasm, with a nucleus and chlorophyll-grains. Below each 

 of the larger hairs the collenchyma gives place to short, thin- 

 walled parenchyma, which, together with the epidermis covering 

 it, forms those emergences on the summit of which the hair 

 is seated. Within this is 



3. Thin-walled cortical parenchyma, the cells of which are 

 shorter, but wider, than those of the collenchyma ; there is, 

 however, no sharp limit between them : observe transitional 

 forms. The cell-contents resemble those of (2), but there is less 

 chlorophyll. 



Note the resin-passages, the course of which is directly 

 longitudinal : they therefore appear as longitudinal bands of 

 small, oblong, thin-walled cells (epithelium). 



The bundle-sheath may occasionally be recognized as the 

 layer of cells immediately outside the bundle. Very commonly 

 starch-grains may be detected in its cells. 



4. The vascular bundle. Supposing the section to have been 

 approximately median through the bundle, the following com- 

 ponents will be found to be included in it : 



i. Hard bast, sclerenchyma, or bast-fibres, which appear in 

 longitudinal section as long prosenchymatous cells, occasionally 

 divided by more or less oblique septa. Walls thick, lignified 

 (yellow with chlor-zinc -iodine, or with acidulated aniline 



