MICROSCOPIC OBJECTS. 



Fig. 15. Transverse Section of the Stem of the Garden 

 Rhubarb (Rheum undulatum), x 30. 



This transverse section of the Rhubarb is drawn to show 

 the natural position of the vascular tissue when seated in 

 a mass of cellular tissue. The dark spots illustrate the 

 fibro-vascular, and the lighter formation (which is composed 

 of cells) the cellular tissue. For a description of the vascular 

 tissue, see fig. 16. 



This should be mounted in the dry state. 



Fig. 16. Spiral-vascular Tissue from Garden Rhubarb 

 (Rheum undulatum), x 120. 



Fibro-vascular tissue comprises fibro-vascular bundles, ves- 

 sels, ducts, &c. The drawing shows the spiral -vascular tissue 

 as seen in bundles when taken from the Rhubarb and other 

 plants. This tissue is most important in the growth of young 

 plants, as it then appears to conduct the juices of the plant. 

 Spiral-vascular tissue is characterized by a spiral formation of 

 the secondary deposit ; and forms elongated, acuminated cells 

 or vessels, which generally communicate with each other. The 

 spirals are generally single, but occasionally double &c. (see 

 fig. 17). In some vessels these are replaced by rings, when 

 they are called annular. Spiral tissue was formerly called 

 trachenchymatous, from the supposed resemblance to the air- 

 vessels of insects (see dissections of Insects). Scalariform 

 tissue is a kind of spiral- vascular tissue (see fig. 12). 



This object should be mounted in liquid. 



