PLANT TISSUES IIQ 



Xylem is that part of a fibro-vascular bundle that contains wood 

 cells and fibers. It may also contain tracheae, tracheids, seldom 

 sieve tubes. 



Phloem is that part of a fibro-vascular bundle that contains sieve 

 tubes, phloem cells, and often bast fibers. 



SECRETION SACS (SECRETION CELLS) 



These were formerly parenchyma cells which sooner or later lost 

 their protoplasm and nucleus and became receptacles for oil, resin, 

 oleoresin, mucilage or some other secretory substance. They are 

 generally found in parenchyma regions of stems, roots, leaves, 

 flower or fruit parts and frequently possess suberized walls. Good 

 illustrations of these structures may be seen in Ginger and Calamus. 



INTERCELLULAR AIR SPACES 



Intercellular air spaces are cavities filled with air found between 

 cells or groups of cells throughout the bodies of higher plants. Their 

 function is to permit of the rapid movement of atmospheric gases 

 through the entire plant body. They are formed either by the 

 breaking down of the middle lamella of the cell walls, where several 

 cells come together, and a later separation of the cells at these 

 places (Schizogenous inter cellular- air- spaces), or by a breaking down 

 and disappearance of cell walls common to groups of cells (lysigenous 

 intercellular-air-spaces). In terrestrial plants which live in middle 

 regions (mesophytes) and in desert plants (xerophytes) the intercellu- 

 lar-air-spaces are averagely small and more or less angular. In 

 plants of swamp or marsh habit they are medium-sized, while in 

 those which live entirely in the water (hydrophytes) they are of large 

 size and more or less rounded. 



SECRETION RESERVOIRS 



These structures are either found as globular or irregular spaces, 

 as in Orange and Lemon Peel and Eucalyptus leaves, containing oil 

 or oil and resin when they are called internal glands, or, as tube-like 

 spaces filled with hydrocarbon principles such as are found in Pine 

 leaves and stems, when they sometimes receive the name of secretion 



