02 ELEMENTARY T188VE8, 



PREPARATION : Suitable sections can be obtained by fastening 

 small portions of these steins in the jaws of a microtome ;ui<l 

 sectioning with a stout razor. Several radial-longitudinal sections 

 of each should be obtained in order to be certain of including 

 the proper portion (xylem) of the fibro-vascular bundle. 



Other material than that suggested above can be used, but 

 such common plants have been selected as are found to show 

 the desired structure. These specimens should be examined with 

 reference to the study of the general forms indicated in the illustra- 

 tions of Tracheae 'which follow. Vines' Text Book of Bot., p. 

 135 ; Gopdale, p. 82 ; DeBary, p. 165. 



The Tracheids of Coniferae. 



Illustration: Wood of WHITE PINE (/V////.S .s?/W>//x). The 

 seasoned sap-wood of a young Pine answers the best for the study. 



PREPARATION FIRST: Make several thin longitudinal sections 

 at right angles to the "grain" (the annual layers.) Mount in 

 water. 



OBSERVE : 1. The Tracheids, oblong and fusiform like wood 

 fibres, but showing " bordered pit* " at intervals. This form of 

 Tracheid is found throughout the Gymnosperins, fossil and living. 



2. The outer and inner ring of the bordered pit. ^By focus- 

 ing, the inner ring or outline of the lumen on the oppwHle side of 

 the pit may be seen. 



3. The rows of rectangular cells occasionally crossing the 

 Tracheids at right angles. These are portions of the Medullary 

 Rays. 



PREPARATION SECOND: (1.) Make several thin longitudinal 

 sections parallel to the "grain." (2.) Make several thin cross- 

 sections. Mount (1) and (2) in water under the same cover. 



OBSERVE in (1.) 1. The small cavities, occurring along the 

 common-wall of two Tracheids. These are single and lens-shaped 

 the bordered pits seen in section. 



2. Look for the middle lamella or " limiting membrane " 

 which originally separated the two halves of the pit and was con- 

 tinuous with the common-wall of the two Tracheids. 



3. The row of roundish or angular cells three to six in 

 number occasionally seen between Tracheids. These are large 1 " 



