82 POWDERED VEGETABLE DRUGS 



Porous : Very variable in transverse diameter. The pores vary 

 in form and size, gradually merging into the reticulate type. 

 Pores slit-like (transverse and diagonal); cats-eye (slits with 

 borders), circular, oval, etc. Very widely distributed among 

 herbs, shrubs, trees (conducting tubes of woody tissues). 



Scalariform: Typically developed in the fern group. Less com- 

 monly present in other plant groups. 



Reticulate : A modification of the porous type. Very common in 

 dicotyledonous herbs. Very variable in transverse diameter. 

 Gradually merging into the spiral type. 



Spiral: Typically developed in monocotyledonous plants, though 

 also common in dicotyledons. Gradually merging into the 

 annular type. 



Annular: Typically developed in the grass family; less common in 



other plant groups. 



PARENCHYMATOUS TISSUE. A term applied to the predominating tissue 

 in plants or in plant parts. We thus speak of k wood parenchyma, 

 bark parenchyma, leaf parenchyma, seed parenchyma, fruit 

 parenchyma, etc., etc. The following types are recognized, in a 

 more limited sense. 



Parenchyma Proper: The cells are practically isodiametric, thin- 

 walled, walls only slightly porous and never lignified. There are, 

 as a rule, intercellular spaces due to the fact that the cells are 

 loosely united. Widely distributed in the plant kingdom, occurs 

 in roots, stems, fleshy fruits, tubers, rhizomes, bulbs and corns. 



Pith: The central tissue of stems, rhizomes and roots. A typical 

 parenchyma. 



Bark Parenchyma : Cell-walls may be suberized (cork-tissue) , often 

 not suberized (inner bark parenchyma). 



Endosperm Tissue : The parenchyma of seeds. Cells extremely 

 variable as to the thickness of walls, porosity of walls, contents. 

 Often a highly diagnostic tissue. 



Fruit Pulp (of false as well as true fruits) : A typical parenchyma. 



Pericarp Parenchyma : Generally a typical parenchyma. 



Leaf Parenchyma or Spongy Tissue : Composed of from one to three 

 rows of palisade cells (upper, sometimes also a lower, as in Eucalyp- 

 tus), and the aerating, pneumatic or spongy tissue proper. Very 

 rarely diagnostic. Cell-contents sometimes diagnostic (crystals, 

 resin, coloring substances, etc.). 



SIEVE TUBES. ---Associated with vascular bundles, typically de- 

 veloped in cucurbitaceous plants, of no special diagnostic value. 



