X] 



LEAVES OF CALAMITES. 



381 



epidermal layer with a limiting cuticle. Internal to this we 

 have radially elongated parenchymatous cells forming a loose or 

 spongy tissue, the cells being often separated by fairly large spaces 



Pig. 86. A leaf of Calamites. 



1. Transverse section; t, vascular bundle; a;, aheath of cells, x 35. 



2. Vascular bundle consisting of a few small tracheids, t. 



3. A tracheid and a few parenebymatous cells, the latter with nuclei. 



4. A stoma; s, s, guard-cells. 



5. PaUisade cells and intercellular spaces. 



From a section in the Manchester Museum, Owens College. 



(fig. 86, 5), especially in the region of the blunt lateral wings of 

 the leaf Some of these cells contain a single dark dot, which 

 in all probability is the mineralised nucleus. These pallisade- 

 like cells probably contained chlorophyll and constituted the 

 assimilating tissue of the leaf In the centre there is a circular 

 strand of cells limited by a layer of larger cells with black 

 contents, enclosing an inner group of small-celled parenchyma 

 and traversed by a few spiral or scalariform tracheids constituting 

 the single median vein. It is hardly possible to recognise any 

 phloem elements in the small vascular bundle ; there appear to 

 be a few narrow tracheids surrounded by larger parenchymatous 



