6 STUDIES IN HISTOLOGY. 



blue. Soon the inner and middle plates dissolve, the outer not 

 being attacked until somewhat later. If Schulze's macerating 

 solution (full strength) is employed, the outer plate dissolves 

 quickly, but the others are not much affected for some time. 

 Careful management of these powerful solvents is demanded to 

 insure even a moderate degree of success in this demonstration. 



V. BAST-FIBRES. 



Isolation of these cells is easily effected by teasing with needles 

 under the dissecting microscope. The use of macerating solu- 

 tions for this purpose is also admissible, but the results are not 

 quite so satisfactory as with the wood-elements. Examination 

 of the table on page 90 shows the wide difference which exists 

 between the dimensions of the raw fibres and their structural 

 elements, into which they can be separated mechanically. 



Most bast-fibres take the coal-tar colors very well, and it would 

 be best for the student (without giving too much time to it) to 

 note the different effects which are produced on various fibres by 

 the colors described on page 19. The changes produced in the 

 dimensions of the fibres b} T dilute acids should also be observed. 

 After this preliminary practice the reactions given on page 90 

 should be carefully repeated with such material as is at hand. 

 Full directions for the preparation and use of the prescribed 

 reagents will be found in the introductory chapter. Lastly, de- 

 terminations of the average dimensions of the commercial fibres, 

 flax, hemp, jute, etc., should be carefully made. 



VI. CRIBROSE-CELLS OR SIEVE-CELLS. 



These can be very easily demonstrated in thin vertical sec- 

 tions of the stems of an}* large Cucurbitaceous plants ; for in- 

 stance, squashes, melons, etc. If the student fails to detect in 

 fresh material forms similar to those shown in Fig. 73, a little 

 tincture of iodine should be added to the specimen, in order to 

 contract the lining and other contents of the cells. By this 

 reagent the contents become more or less distinctly colored, and 

 the discrimination between the cells and the surrounding tissues 

 is generally very plain. In other common plants, grape-vines, 

 etc., the detection of cribrose-cells is not always easy, but a 

 diligent search will bring out these characteristic constituents of 

 soft bast. 



The study of the structure of the sieve-plates requires the use 

 of much higher powers of the microscope than most beginners 



