s^ 



ANATOMY AND PHYSIOLOGY OF 



Fig 38. 



' (t 



CoUenchynia cells from the 

 stem of Beta^ vulgmis In 

 the angles of the cellb the 

 substance of their membrane 

 (a) IS very hygroscopic, and 

 swells np ^elatmously m 

 WAter. 



made out wlietlier or not, in certain case^, for instance in tlie albnmen 

 of ScMzolohmm excelsum {see Scliloiden on ^^ Albumen'' in the " JS^ova 

 act Natm\ Curios'' xix. p. 11, pi. xliii, ^g 55), cells and intercellular 

 substance originate together; but nothing can be decidedly determined 

 about this, since we are altogether -without observations on the develop- 

 ment. 



In very many cases it is extraordinarily difficult to distinguish the in- 

 tercellular substance from the cell-wall. In regard to this, my opinions 



differ in many cases from those of many other ob- 

 servers ; for instance, of Schleiden, especially in re- 

 lation to the structure of the cells which swell up 

 in a jelly-lii:e manner in water (the so-called coUen- 

 chyma-cells), which occur in the outer layer of the 

 rind in many plants ; for example, in Cuairhita 

 Fepo, and Beta vulgaris (fig. 38), in which, accord- 

 ing to my view, the parts swelling up (a) belong 

 to the cell-membrane, and are formed of second- 

 ary layers deposited in the angles of the cells ; 

 while, according to the opinion I formerly ex- 

 pressed, still defended by Schleiden, the cells possess 

 walls of uniform thickness, and the laminated mass 

 lying between their angles is to be regarded as in- 

 tercellular substance. In such difficult cases it is 

 best to allow the cells to swell up in nitric acid, to 

 render the stratification of their membrane more dis- 

 tinct, and thus to make out the position of the primary membrane (^g. 39). 

 linger ('^ Bokm. Zeitung," 1847, 289) has recently sought to demon- 

 strate that the origin of the intercellular substance and of the cells is 



simultaneous. The reasons advanced by him do 

 not seem to me convincing. In the present state 

 of our knowledge, however, we can say very little 

 about this ; the whole theory of the intercellular 

 substance requires a thoroughly new investigation. 

 The membrane secreted upon the surface of cells 

 exhibits most remarkable conditions, since no inter- 

 nal organization or composition from different layers 

 can be detected in it, while it is yet very frequently 

 clothed in an extremely complicated manner with 

 reticulated projecting ridges, straight or waving 

 lines, or granular or spiny projections, as is seen in 

 the most varied and elegant manner on many 

 spores and pollen-grains. Linear projections also 

 occur frequently upon the cuticle, and these are by 

 no means arranged in correspondence with the sub- 

 jacent celk It is not at present known of wtat chemical compound 

 these membranes are composed ; cellulose is not found in them. 



The structure and origin of the cuticle, and the epidermis-cells lying 

 beneath it, have been the subjects of manifold discussions. "When an 

 epidermis, especially one from the upper side of a leathery leaf, is sliced 

 transversely, the walls of its cells turned outwards are seen to be much 

 thicker than the rest. Iodine and sulphuric acid either colour the whole 

 of this outer wall dark yellow, and sulphuric acid does not dissolve it, or, 



Fuj 39. 



— 'f 



The point of imion of four 

 cells of Betco swollen np m 

 hydrochlonc acid It shews 

 the uniform dense teitiary 

 layer (h) , the gelatinous 

 secondary layers (a); and 

 the pnmary membrane (e). 



