242 ANNUAL OF SCIENTIFIC DISCOVERT. 



tion being properly established. The examination of the vegetable cellular 

 membranes possesses, however, very great interest both to the chemist and 

 the vegetable physiologist. We see, in fact, these membranes undergo, dur- 

 ing vegetation, some remarkable modifications; in certain cases their thick- 

 ness increases rapidly, while in other cases it diminishes in as notable a 

 manner. The latter phenomena is presented during the ripening of almost 

 all fruits. The cell walls of green fruit are at first ver} 7 thick, and formed 

 of several concentric membranes; at the period of maturation, however, 

 these walls become rapidly thin, as indicated by the changes which take 

 place in the hardness and transparency of the fruit. It can also be rigor- 

 ously determined by analysis. The following are the results of the exam- 

 ination of the solid pericarp of two species of pears, taken at different 

 periods of their development and maturation : 



Percentage of membraneous tissue. 

 "Winter pear. Summer pear. 



Juno 16 17-7 13-4 



" 24 17-4 13-4 



July 1 14-8 11-0 



" 9 14-0 11-0 



" 17 12-5 11-0 



" 26 9-2 6-7 



August 4 5-8 6-0 



" 12 4-8 5-1 



" 20 3-8 5-4 



" 28 34 3-5 



Similar analyses to the preceding were made upon fruits, such as apples, 

 which ripen after they are detached from the tree, and which do not alter in 

 size during maturation. From these experiments it results that the cell 

 walls in these fruits undergo a notable diminution of weight during the 

 period of maturation; it therefore became interesting to know Avhat were 

 the membranes in the cell walls which were thus absorbed at a certain pe- 

 riod of the growth. M. Fremy, several years back, showed that vegetable 

 tissue contains an insoluble substance, which he named pectose, constantly 

 accompanying the cellulose, and that under very slight influences this body 

 becomes soluble, and is converted into pectim. This modification explained 

 the origin of a gummy substance which appears in the juice of fruit which 

 has ripened or has been decocted ; and it appeared probable that the intei'ior 

 membranes of the cell, which become altered, are composed of pectose, 

 whilst the exterior membrane is formed of cellulose, which is a very stable 

 body. The solvent for cellulose, cuprate of ammonia, discovered by M. 

 Schweitzer, and successfully employed by M. Peligot in determining the 

 composition of the skin of silkworms, afforded the means for ascertaining 

 the chemical nature of the walls of vegetable cells. The ammoniacal solu- 

 tion of copper may be prepared by the dii-ect action of solution of ammonia 

 and atmospheric air on metallic copper, or by dissolving hydrated oxide of 

 copper in caustic ammonia. The solution prepared in either of the above 

 ways is a perfect and immediate solvent for cellulose. To determine with 

 this reagent the composition of the vegetable cells, thin slices of fruits or 

 roots are cut up and left to digest for some hours in the solution. The cells 

 assume a green color, swell out, and appear to disaggregate. After the 

 action of the reagent, the tissue, examined under the microscope, had pre- 

 served its original form, but the outline of the cells was less distinct. Ill 

 these experiments care was taken to employ tissues which contained no 



