SUNFLOWER. STEM. 51 



development of the stem, and the point at which the 

 section is taken, the bundles may be more or less 

 completely joined laterally with one another. In old 

 stems, and at or near the nodes this lateral fusion is 

 most complete : still, under any circumstances the 

 originally separate bundles can easily be recognised. 



Centrally, i.e., within the ring of vascular bundles 

 is 



5. The parenchymatous Pith, consisting of thin- 

 walled cells, which have for the most part lost their 

 cell-nature (i.e. have no protoplasmic contents), and 

 are filled with air: hence the whiteness of the fresh 

 pith. (N.B. In material, which has been a long time 

 in spirit, the air may have been removed by the alcohol, 

 but this is usually a slow process.) 



II. Choose out the thinnest of the sections, and 

 examine it with a higher power (one-sixth inch or 

 one-eighth inch), starting as before from the periphery 

 of the stem. 



1. The Epidermal Layer will be seen to consist 

 of cells contiguous with one another, without inter- 

 cellular spaces (excepting occasional stomata, which 

 are, however, rare ; cf. infra). The walls, and especially 

 the external and internal walls, are thick, highly 

 refractive, and show a stratified structure. In Schulze's 

 solution they are blue (cellulose) with the excep- 

 tion of the outermost layer the cuticle : this is a 

 continuous, well-defined layer, which stains yellow, 

 and may thus be easily recognised. 



The granular protoplasmic contents of these cells 

 (brown, Schulze's solution) are not plentiful, but form 

 a thin layer lining the somewhat rounded cell-cavity. 



E 2 



