64 GROUPS OF TISSUES, OR TISSUE SYSTEMS 



(/) Reduced bundles and bundle endings can be studied in 

 leaves and petals by placing them in some clearing fluid, e.g. a 

 mixture of phenol (carbohc acid), and turpentine after 15 to 20 

 minutes' treatment with 95 per cent alcohol. Mount in the 

 same fluid and examine under low and high powers. If these 

 objects are previously placed with their cut ends in an aque- 

 ous safranin or eosin solution until the colored Hquid has 

 filled the bundles these are more conspicuous. 



(w) Examine the cut ends of logs and stumps of various kinds, 

 to distinguish the heart wood and sap wood. That they are 

 different in some of their chemical characteristics will be shown 

 by their different proneness to decay. 



94. The Supporting System. In many plants the 

 supporting and conducting systems are intimately 

 connected, the vascular bundles containing not only the 

 conducting cells but also an abundance of wood and bast 

 fibers. However, at first the stems are often supported 

 by other means. Thus, a strong development of 

 coUenchyma strands under the epidermis is a very com- 

 mon occurrence. By the natural turgor and growth 

 of the stem, these collenchyma strands are stretched, 

 and thus stiffen the stem until the fibrous tissues 

 are developed later in connection with the vas- 

 cular bundles. In the cortex, bast bundles are fre- 

 quently encountered, inde- 

 pendent of any vascular 

 bundles. In the stems of 

 Ferns and Fern Allies, large 

 bundles of fibrous tissues are 



in 



(3) scattered here and there. 

 Closely allied to the support- 

 ing system of tissues, in function, are those tissues that 

 serve for protection, as for example, the sclerenchyma, 

 deposited in various parts of the plant, such as the 

 bark, roots, fruits, and seeds. 



Fig. 31. — Supporting system 

 stems of 'fl) moss, (2) fern, 

 flowering plant. 



