148 



PLANT ANATOMY. 



The parts of the pistil have already 

 been considered. In the study of the 

 mature pistil, in particular the seeds, a 

 great deal could be ^v^itten of the nu- 

 merous modifications that take place in 

 the cells of these parts. In general they 

 belong to the parenchymatic type, while 



the chief interest in them is the great 

 amount of thickening and distortion that 

 takes place. The changes that take place 

 during fertilization are of interest from 

 a scientific botanical standpoint rather 

 than from a practical analysis point of 

 view. 



CHAPTER X. 



MICRO-CHEMICAL REACTIONS. 



It is far from the purpose of the pres- 

 ent chapter to do any more than to point 

 out in as brief a manner as possible 

 some of the more important micro-chem- 

 ical reactions of plant structures or con- 

 tents; the student who would follow 

 them out to any further detail is referred 

 to "Botanical Micro-technique," by Zim- 

 merman, H. Holt & Co., and Hervey's 

 translation of the "Microscope in Bot- 

 any," by Behrens. In these volumes a 



full consideration of the subject will bo 



found, with copious bibliographical ref- of reference already quoted. 



properties. They are insoluble in sul- 

 phuric acid, are colored yellow or brown 

 by chlor-iodide of zinc, and iodine and 

 sulphuric acid. Concentrated caustic po- 

 tash causes a yellowish coloration which 

 becomes more intense on heating. 



^Mucilaginous Modification. This can 



L . J 



be readilv detected by the extreme de- 

 gree of swelling that takes place on the 

 addition of water. The various gums 

 have a number of different reactions 

 which must be sought for in the works 



erences. 



Tests for Cell Walls. It has already 

 been pointed out that the cell wall may 

 undergo at least five modifications from 

 its chemical basis of cellulose. Each of 

 those has some micro-chemical tests that 

 are of value. 



Cellulose. Strong sulphuric acid 

 causes cellulose to swell, turn blue and 

 dissolve. Schweizer's reagent, cupra- 

 ammonia, dissolves cellulose completely. 

 It should be made fresh, as it does not 

 keep well. Iodine and sulphuric acid 

 give a blue color. Chlor-iodide of zinc, 

 blue to violet coloration. Hematoxylin 

 in weak solution stains cellulose wall 

 blue to black, depending upon the time 

 of staining. I prefer Delafield's solu- 

 tion for this purpose. 



Lignification. Lignified cell walls are 

 insoluble in Cupra-ammonia, and they 

 color yellowish to brownish by Chlor- 

 iodide of Zinc or Iodine and Sulphuric 

 acid. Several aromatic compounds, as 



Phenol, Thymol, Orcein, Aniline, Phloro- 

 glucin, etc., give characteristic reactions. 

 (See table Zimmerman, p. 141.) IMilo- 

 roglucin in water or alcoholic solution, 

 preceded or follow^ed by dilute Hydro- 

 chloric acid, gives a beautiful cherry- 

 red coloration to lignified cell mem- 

 branes. Fuchsia stains lignified cell 

 walls a deep and persistent red. 



Cutinized and Suberized Cell Walls 

 have about the same micro-chemical 



Tests for Cell Conients. 

 Nitrogenous Contents: Protoplasm. It 



has already been pointed out that the 

 albumenoids of the plant are numerous 

 and very complex, and a great many 

 characteristic reactions have been found 

 for different members of this general 

 group. Only those general reactions will 

 be here mentioned that have been in long 

 use. With iodine the protcids take on a 

 yellowish or brownish or even black col- 

 oration, according to the strength of the 

 solution. Concentrated nitric acid gives 

 a yellow color, the Xantho-protelc reac- 

 tion, and Millon's reagent (a mixture of 

 mercuric and mercurous nitrate with ni- 

 trous acid, prepared by dissolving one 

 part of mercury in two parts of nitric 

 acid and then diluting with twice the 

 volume of water) colors proteids red in 

 various shades ; slight warming brings 

 out the reaction more rapidly, 



Aleurone grains. In searching for 

 aleuroue grains the previous treatment 

 of the sections is of importance. They 

 should not touch water in any form, as 

 aleurone is soluble in that medium. The 

 material to be investigated should first 

 he fixed, preferably with absolute alco- 

 hol or picric acid alcohol, and then treat- 

 ed according to the desire of the investi- 

 gator to bring out the inclusions or the 

 fundamental mass or ground substance 

 of the grains. To bring out the ground 

 mass, staining in an alcoholic solution of 



