122 



BOTANT. 



of one or more tissues; this reduction may be so great as to 

 leave but a single tissue, which in many cases is composed of 

 only a few spiral vessels or tracheides (Fig. 109). In other 

 cases, instead of spiral vessels the bundle may consist of a few 

 fibres of bast ; or of elongated, thin-walled cells, which are 

 doubtless to be regarded as meristem-cells which failed to 



fully change into one of the or- 

 dinary permanent tissues ; this 

 last is a very common accom- 

 paniment of reduced bundles. 



{a) In tlie study of the structure- 

 of fibro-vascular bundles much care 

 is required in tbe preparation of tba 

 specimens. The thin transverse sec- 

 tions are obtained by ordinary pro- 

 cesses with no great difficulty, but 

 such is not the case with the lon- 

 gitudinal sections ; they must not 

 only be extremely thin, but must run 

 parallel with the cells and fibres, 

 and moreover, must be sufficiently 

 large to show all, or a considerable 

 part, of the bundle. It is necessary 

 also to have several longitudinal 

 sections, and to know the exact posi- 

 tion of each one when compared 

 with the transverse section. 



(ft) The most satisfactory results 

 can be obtained only by the use of 

 some mechanical section-cutter.* In 

 most cases the sections are made 

 more easily after soaking the stems, 

 roots or leaves used in alcohol. 



(c) In many cases it is profitable 

 to macerate some of the lono^itudi- 

 nal sections in nitric acid and potassi- 

 um chlorate (Schulze's maceration), 

 so as to permit of an isolation of the fibres, cells, and vessels. 



(d) Good specimens for study may be obtained from any of the 

 higher plants, but the examination will be most profitable if the order 



* For the various contrivances used for cutting sections see the com- 

 mon books on microscopy, also American Naturalist, 1874, p. 59 ; 

 American Quarterly Microscopical Journal, 1879, p. 131, and several 

 articles in Qr. Jour. Mic. Science, 1870, 1874, 1875, 1877. 



Pig. 109. — Terminal ramifications of 

 the reduced fibro-vascular bundles of 

 the leaf of Psoralea bitumiriosa; the 

 ends X , X , are cut off" in making the 

 preparation, the others are the actual 

 termini ; the bundles are seen to be 

 composed of spiral tracheides, and 

 spiral vessels resulting from their fu- 

 sion ; around the bundles are f^een the 

 cells of the chlorophyll-liearins paren- 

 chyma. X 225.— After De Bary. 



