

SUN FLOWER STEM 7 1 



To complete the study of the tissues it would be necessary also 

 to cut tangential sections : in the case of tissues in which the 

 radial differ from the tangential walls, such sections must be made, 

 and the comparison drawn between them and the transverse and 

 radial sections. In the present case, however, this is hardly 

 necessary, since the individual components of the several tissues 

 of this stem appear almost uniform in their tangential and 

 radial aspects. 



Starting as before from the periphery, note succes- 

 sively 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 dis- 

 turbance 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 cellu- 

 lose walls (blue, chlor-zinc-iodine), and thin transverse 

 ends : the contents are protoplasm, with a nucleus and 

 chlorophyll-grains. Below each of the larger hairs 

 the collenchyma gives place to short, thin-walled paren- 

 chyma, 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 collen- 

 chyma ; there is, however, no sharp limit between 



