274 Prof. H. Karsten on the Formation, 



I have repeatedly observed, for example, in the wood of Cin- 

 chona, 



Among the large cells of the vertically elongated parenchyma 

 of the stem of Philodendron, some scattered rounded cells are 

 met with almost completely filled with a large crystalline mass 

 of oxalate of lime. In these cells also, when occurring in a mass 

 of cork-tissue, some young cells are seen to originate between 

 the crystalline mass and the parent cell, which, after having 

 acquired their full dimensions, have a cellulose composition, and 

 ultimately become converted into cork. These cells so entirely 

 surround the crystalline mass that it appears to be enclosed 

 within an envelope of small irregularly shaped cork-cells inter- 

 vening between it and the parent cell-wall (fig. 2 k). 



Besides these kinds of cells, which all contribute to the cica- 

 trization of the cut surface by the formation of cork, two other 

 elementary organs are encountered in the tissue o^ Philodendron; 

 in these no cell-development takes place, but they become ab- 

 sorbed within the layer of cork-cells. The first of such organs 

 are the series of cells, united with fibres and filled with raphides, 

 which are found dispersed in the parenchyma of the bark and 

 of the medulla, and which in other Aroidese contain a milky 

 juice. The second kind are the branching fibrous cells found 

 only in the cortical tissue. Both these structures are, in all 

 probability, principally concerned in the process of secretion — 

 an opinion which I expressed suppositively, in my 'Disserta- 

 tion,' with regard to the thickened secondary membrane ; I also 

 specially mentioned the absorption of the fibrous cells of the 

 bark, in my Memoirs on the Palms and on the China-barks (Die 

 Vegetationsorgane der Palmen, 1847, p. 53, and Die med. 

 Chinarinden Neu- Granada's, 1858). 



These fibrous cortical cells of the Philodendron have a remark- 

 ably ramified form, giving off from each side of the upper and 

 lower extremities of the parallelopipedal and horizontally ex- 

 tended cells two very long and thin branches, which lie free in 

 the comparatively wide intercellular spaces, and end in pointed 

 closed extremities. These long branches, standing out at right 

 angles from the cell, are not produced until after this has at- 

 tained its full size ; and soon after the outgrowth of these pro- 

 cesses the entire cell-wall proceeds to increase in thickness. It 

 can indeed be distinctly made out that these cortical cells, as 

 well as the lacteal vessels, here occupied by raphides, originate 

 from cells, and not from intercellular spaces lined with cell- 

 material. 



In my paper on tannic acid (Monatsbericht der Berl. Akad. 

 der Wissenschaften, 1857) I described the lacteal vessels of 

 Colocasia, Dieffenhachia, and other Aroidese through which a 



