90 ELEMENT. \RY 'I 'ISS UES. 



V. TRACHEABY TISSUE. 



(c) Tracheids like Wood-cells in form, and like ves- 

 sels or Trachece in structural markings. 



(d) Tracheae" Vessels " or " Ducts." 



Type 1 includes Dotted and Handed Ducts, passing 

 into Pitted and Scalariform Ducts by gradations. 



Type 2 includes Spiral, Annular, and J\<ti<- n/itf/ 

 Vessels and their gradation. See Goodale, p. 59 ; DeBary IV. * 



Illustration: For PROSENCHVMA (in its widest sense.) BARK 

 and WOOD of LEATHERWOOD (Dirca palustris.) 



PREPARATION for (a). Remove the brown cuticle from a branch 

 of Leathencood, also the loose cells beneath. Make two or more 

 very thin longitudinal sections of the bark, pulling one end of each 

 section from the branch instead of cutting it. Many of the silky 

 bast-fibers will thus be free at the end. Mount in water. Another 

 mode, is to place bast tissue in nitric acid and potassium chlorate, 

 and heat for a few minutes. The bast fibres can 'then be separated 

 under a dissecting microscope. Use a 3-4 and then a 1-5 

 in. objective. 



ORSERVE : 1. The very long bast-fibres; trace out a free one, 

 and measure its length. 



2. What kind of cells, if any, occur with the bast. 



3. The clear unmarked walls of bast ; the tapering ends when 

 not broken. 



PREPARATION for (b) and (c). Make (1) very thin, tangential 

 sections of wood ; (2) very thin transections of the branch includ- 

 ing wood and bark. Mount in water and stain with haematoxylin. 



In the longitudinal section: 



OBSERVE: 1. The short unmarked, fusiform wood fibres or 

 typical wood -cells whose ends over-lap. Measure the longest. 



2. The fusiform cells marked by spiral lines, dots, bordered 

 pits, etc. Tracheids; see Goodale, Fig. 78, 79; Bessey, p. 81; 

 Bastin, p. 162 ; Vines' Text Book of Bot., p. 182. 



* It will be observed that the classification of 1'rosenchyma tissue is not. the 

 one usually pre>ented. It is believed that by adherini: Hosely to this one in these 

 studies, a correct idea can lie obtained of the development of the more perfect 

 forms of ducts from the simple cells. It is desirable that the chissilicat ions of 

 others be compared and the points of difference noted. 



