SUCTION 16.] 



ANATOMICAL STI;i (TURE. 



133 



these, or the prolongation of others, into hollow fibres or tabes of various buso. 

 Two sorts <>l' .such transformed cells u r <> together, and essentially form the 



Mis. Wood. This is found Lu all common herbs, as well as in shrubs 

 and trees, but the former have much less of it in proportion to the softer 



cellular tissue. It is formed very early in the growth of the root, stem, 

 anil leaves, — traces of it appearing in large embryos even while yel in the 

 seed. Those cells thai lengtheu, and at the same time chicken their walls 

 form the proper WbODI FlBRB or WOOD-CELLS ; those of larger si/.e and 



thinner walls, which are thickened only in certain parts SO as to have 

 peculiar markings, and which often are seen 

 to he made up of a row of cylindrical cells, 

 with the partitions between absorbed or bro- 

 ken away, are called DUCT8, or sometimes 

 \ ESSELS. There are all gradations between 

 wood-cells aud ducts, and between both these 

 and common cells. But in most plants the 

 three kinds are fairly distinct. 



409. The proper cellular tissue, or paren- 

 chyma, 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 numer- 

 rous and crowded that in the stems and 

 all permanent parts they make a solid mass 

 of wood. They extend into and ramify ii 

 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, 



Fie ill. Magnified wood-cells of tin- bark (bast-cells) of Basswood, one and 

 part "i another. 146. Borne wood-cells from tin- wood (and below part of a duet); 

 and 446, a detached wood-cell <>t' tin- same; equally magnified. 



Fig. 117. Borne wood-cells from Bnttonwood, Platanus, highly magnified, a 

 whole cell and lower end of another on tin- left ; a cell cut half away lengthwise, 

 and halt of another on the right ; some pores or pits (a) seen on tin- left; while 

 6 6 mark sections through these on the cut Burface. When living and young the 

 protoplasm extends into these and by minuter perforations connect- across them. 

 In age the pits become open passages, facilitating the pas-a^c of sap and air. 



