FREE BOOKS

Author's List




PREV.   NEXT  
|<   117   118   119   120   121   122   123   124   125   126   127   128   129   130   131   132   133   134   135   136   137   138   139   140   141  
142   143   144   145   146   147   148   149   150   151   152   153   154   155   156   157   158   159   160   161   162   163   164   165   166   >>   >|  
larger size and thinner walls, which are thickened only in certain parts so as to have peculiar markings, and which often are seen to be made up of a row of cylindrical cells, with the partitions between absorbed or broken away, are called DUCTS, or sometimes VESSELS. There are all gradations between wood-cells and ducts, and between both these and common cells. But in most plants the three kinds are fairly distinct. [Illustration: Fig. 444. Magnified wood-cells of the bark (bast-cells) of Basswood, one and part of another. 445. Some wood cells from the wood (and below part of a duct); and 446, a detached wood-cell of the same; equally magnified.] [Illustration: Fig. 447. Some wood cells from Buttonwood, Platanus, highly magnified, a whole cell and lower end of another on the left; a cell cut half away lengthwise, and half of another on the right; some pores or pits (_a_) seen on the left; while _b b_ mark sections through these on the cut surface. When living and young the protoplasm extends into these and by minuter perforations connects across them. In age the pits become open passages, facilitating the passage of sap and air.] 409. The proper cellular tissue, or _parenchyma_, is the ground-work of root, stem, and leaves; this is traversed, chiefly lengthwise, by the strengthening and conducting tissue, wood-cells and duct-cells, in the form of bundles or threads, which, in the stems and stalks of herbs are fewer and comparatively scattered, but in shrubs and trees so numerous and crowded that in the stems and all permanent parts they make a solid mass of wood. They extend into and ramify in the leaves, spreading out in a horizontal plane, as the framework of ribs and veins, which supports the softer cellular portion or parenchyma. 410. =Wood-Cells, or Woody Fibres=, consist of tubes, commonly between one and two thousandths, but in Pine-wood sometimes two or three hundredths, of an inch in diameter. Those from the tough bark of the Basswood, shown in Fig. 444, are only the fifteen-hundredth of an inch wide. Those of Buttonwood (Fig. 447) are larger, and are here highly magnified besides. The figures show the way wood-cells are commonly put together, namely, with their tapering ends overlapping each other,--spliced together, as it were,--thus giving more strength and toughness. In hard woods, such as Hickory and Oak, the walls of these tubes are very thick, as well as dense; while in soft woods, such as White
PREV.   NEXT  
|<   117   118   119   120   121   122   123   124   125   126   127   128   129   130   131   132   133   134   135   136   137   138   139   140   141  
142   143   144   145   146   147   148   149   150   151   152   153   154   155   156   157   158   159   160   161   162   163   164   165   166   >>   >|  



Top keywords:
magnified
 

Basswood

 

lengthwise

 

Buttonwood

 

highly

 
commonly
 
leaves
 

Illustration

 
cellular
 

parenchyma


tissue

 

larger

 
softer
 

portion

 
consist
 

scattered

 
hundredths
 
thousandths
 

supports

 

shrubs


Fibres

 

extend

 

ramify

 

spreading

 

framework

 

numerous

 

crowded

 

horizontal

 

permanent

 

strength


toughness

 
giving
 

spliced

 

Hickory

 

hundredth

 
fifteen
 

diameter

 
comparatively
 

figures

 
tapering

overlapping
 

thinner

 
thickened
 
broken
 

absorbed

 

called

 
partitions
 

living

 
surface
 

cylindrical