24i ANATOMY AND PHYSIOLOGY OF 



uiiderbtood, it is tlie more general custom to apply tlie term pit (tiipfe!) 

 to the canals perforatmg the secondary layers, and closed externally by 

 the outer membrane of the utricle, and the term pore to the same canals 

 when the primary membrane has been absorbed and the orifices of the 

 utricles open freely into each other. Schleiden, on the conti^ary, uses the 

 name of porous instead of pitted (getupfelten) cells, calls the pits pores, 

 and the pores holes (locher), because {^^ BeitragCj' i 189) according to 

 Adelung and Hemsius, the word tuj^fel (dot) means a shallow depres- 

 sion, or a slightly elevated spot upon a surface. I will not enter mto 

 any etymological controversy against such authorities, but keep simply 

 to my Swabian German, and am consequently of opimon that a panther's 

 skin is geti(/pft (spotted or dotted), although its spots are neither depressed 

 nor elevated * 



c. Chemical Conditions. 



The basis of the memlbranes of all the elementary organs of 

 vegetables consists of neutral hydro-carbons ; in almost all cases, 

 and perhaps "withont exception, of cellulose. 



Cellulose is colouiless, insoluble in cold and boiling water, 

 alcohol, ether, and dilute acids, almost insoluble in weak alkaline 

 solutions, soluble in concentrated sulphuric acid ; it is converted 

 into dextrine by dilute sulphuric acid at a boiling heat. When 

 imbued with iodine it becomes coloured indigo blue if wetted 

 with water, this colour appears more readily under the conjoined 

 influence of water, sulphuric acid, and iodine. According to Payen, 

 the formula of its composition is C12 H20 Oiq. 



Cellulose probably does not occur in a pure condition in any 

 cell-membrane, since a series of both organic and inorganic com- 

 pounds are deposited within it ; in which fact is to be sought the 

 explanation of the manifold physical and chemical differences 

 which are exhibited by the membranes of the same cell at different 

 periods of their age, as well as by the cells of different plants. 



The combination of ceU-membrane with inorganic substances is 

 a very general condition, for the only examples of exception to 

 this which have as yet been met with, are a few species of Mould 

 Fungus (Mulder), into which, however, ammonia might still have 

 entered as a substitute for the fixed bases. In all other plants a 

 skeleton (the ash), corresponding to the form of the membrane, 

 and composed of the alkalies, earths, and metallic oxides which 

 had been deposited in it, remains behind after the cell has been 

 burnt. The younger an elementary organ is, the more abundant, 

 in general, the alkalies appear to be ; the older it is, the more 

 exclusively the earths and metallic oxides seem to be combined 



* Some confusion exists also in our English terminology, the terms 

 dotted and pitted tissues are indifferently applied to these structures, called 

 by the Germans getvp/elt. I have used the v^ord pitted throughout this 

 translation to express this term, because it indicates the true structiu:^. 



