TISSUE SYSTEMS 257 



416. SCLERENCHYMATOUS OR SCLEROTIC TISSUE. 

 Sclerenchyma cells are hard, not elongated, often some- 

 what spherical, and their thickened walls are provided 

 with simple or branching canals. The cells of this tissue 

 are illustrated by the common grit cells of the pear and 

 some other fruits. They are also found in the coats of 

 many seeds, in nut shells, in the pith of some plants. 

 Hold a large gritty part of a pear between two pieces of 

 smooth elder pith or cork and make free-hand sections. 

 Mount in water. Make a drawing of a single cell showing 

 thickness of wall, size of central cavity, wall markings. 

 Note the general shape of the cells. 



417. LATICIFEROUS TISSUE. That tissue found in many 

 plants which contain a milky liquid is called laticiferous 

 tissue. There is no fixed type for the vessels which carry 

 this fluid, as they vary greatly in different plants, being 

 simple in the asclepias (milk weed), and complex in the 

 dandelion. 



418. TISSUE SYSTEMS. The parts of complex plants 

 may be conveniently grouped into three tissue systems : 

 (1) Fibro-vascular tissue system. This is composed of 

 fibro-vascular bundles. The fibrous framework of roots, 

 stems, and leaves is made of fibro-vascular bundles. 

 (Fibro-vascular means fibrous or long and slender, and 

 having long openings or channels.) Each bundle is 

 composed of two fundamental parts: phloem and xylem. 

 The bast fibers may or may not be present. Phloem is 

 another name for the soft bast or sieve tissue, while xylem 

 is the name of the lignified or woody part and is com- 

 posed chiefly of the wood cells, tracheids, and ducts. In 

 stems of dicotyledons (exogens), these two parts of the 

 bundle are separated by cambium, a meristematic layer giv- 

 ing rise to xylem on one side and to phloem on the other. 

 For types of bundles, see next chapter. (2) Fundamen- 

 tal tissue system. This is composed of the parenchyma- 



