282 



TISSUES 



451.) (4) Vascular tissue, composed of large cells which 

 become confluent end to end, forming long tubes or ducts. 

 (TT', Fig. 454.) From the thickened markings which these 

 cells bear they are named spiral, annular, pitted, scalariform, 

 etc. (Fig. 441.) These vessels are often of considerable 

 length, but are never continuous through the entire plant. 

 Cut a grape-vine stem 2 or 3 feet long. Place one cut end 

 in a glass of water and with the other end in the mouth, 



try to force air 

 through the stem. 

 If not successful, 

 shorten the stem 

 a little. 



479. Scleren- 

 chymatous or 

 Sclerotic Tissue. 

 — Sclerenchyma 

 cells are hard, not 

 elongated, often 

 somewhat spheri- 

 cal, and their 

 thickened walls 

 are provided with 

 simple or branch- 

 ing 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. 



480. Laticiferous Tissue, — That tissue found in many 



451. Longitudinal tangential section of Scotch pine wood, 

 highly magnified. It shows tracheids with bordered 

 pits. The dark cells are cut ends of medullary rays. 



