MICROSCOPIC INVESTIGATIOX. 



199 



germiual matter aud inatured as represented into well-defiued cellu- 

 lar structures. Their enlargement by the mere process of budding would 

 tend not only to fill up the whole air-space, but also to burst the cell- 

 Fio;. 34. walls, destroying the functions 



of the plant; XJ, budding-cells 

 passing through dotted duct- 

 cells : "S, S, S, S, the newly dis- 

 covered fungi-fruit, (concepta- 

 cles.) 



The true mechanical struc- 

 ture of the jotted ducts can 

 only be seen when they are 

 highly compressed. A section- 

 al view of them is shown at 1. 

 They are pentagonal, (five- 

 sided.) When not compressed 

 they appear dotted, as at i. 

 When slightly compressed, as 

 at/. When highly compressed, 

 as at e. They are composed of 

 a lace-work, the openings of 

 which are doubtless covered 

 with a membrane of very trans- 

 parent cellulose. The whole structure is calculated to give great 

 strength with great porosity. Another peculiarity connected with the 

 dotted ducts is worthy of mention. On each angle of the duct a series 

 of very small elliptical cells extend lengthways, as represented at 1 

 and 3, F, giving the ducts great rigidness. These peculiar markings, 

 independent of their uses, are of great value to the microscopist in 

 assisting him to distinguish their relation in minute leaf-buds, &c. In 

 some cases, when tracing the position of spiral and dotted ducts, re- 

 quiring high i^.owers of the microscope, I have found it dilficult to dis- 

 Fig. 35. tiuguish one from the other, 



without destroying the cellu- 

 lar matter surrounding them, 

 which frequently is not desira- 

 ble ; but with a knowledge of 

 these markings the distinc- 

 tion is easily made. With a 

 "section-cutter'' make a very 

 thin slice of a potato, cutting- 

 through the eyes, subject the 

 slice to the action of concen- 

 trated nitric acid about five 

 or ten minutes. The starcli 

 will become transparent. 

 Next place the slice on a 

 microscopic glass slide of suf- 

 ficient size to hold the whole 

 section, place a few drops of 

 gum and glycerine compound 

 on it, over which lay a thin 

 glass and compress the whole slightly; adjust the specimnes prop- 

 erly under a power of from 75 to 200" diameters, when the vascular 

 bundles will be found to be connected with the eyes of the potato. 

 Similar examinations of sections cut at different points will demonstrate 



