122 



BOTANY. 



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 trache'ides (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 the study of the structure 

 of fibro-vascular bundles much care 

 is required in the preparation of the 

 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 result* 

 can be obtained only by the use of 

 Fig. 109. Terminal ramifications of some mechanical section-cutter.* In, 

 the reduced fibre-vascular bundles of mos t cases the sections are made 

 the leaf of Psoralea bitummosa; the ., 



ends x, x, are cut off in making the more easily after soaking the stems, 

 preparation, the others are the actual roots or leaves used in alcohol. 



composed of spiral trache!des<, and (c) In many cases it is profitable 

 spiral vessels resulting from their fu- tn mstC p rst tp cnmp nf flip Innrritiirli 

 sion ; around the bundles are seen the to macerate s( > ine Ot the longitudl- 



cells of the chlorophyll-bearing paren 

 chyma. X 225. After De Bary. 



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. 

 (cf) 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. 



