123 



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 trachoides (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 vei-y common accom- 

 paniment of reduced bundles. 



(a) In the study of the structure 

 of fibro-vascular bundles much care 

 is required in the preparation of the 

 specimens. The tliin 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. 



(S) 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 tlie longitudi- 

 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 Jownnl.lSliQ, p. 131, and several 

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



Fig. 109. — ^Terminal ramifications of 

 the reduced flbro-vascular bundles of 

 the leaf of Psoralea hltummosa; 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 tnicUei'des, and 

 spiral vessels resulting fr'tm their fu- 

 sion ; ai'Cund the bundles are feen the 

 cells of the chlorophyll-beanng paren- 

 chyma. X 325.— After De Bary. 



