FORM OF THE PLANT-CELL. 



65 



into closer contact, always pressing more and more upon each other, 

 until they are quite parallel. They probably originate in parenchyma- 

 tous cells, in the same way as prosenchyma. Between them and the 

 longitudinal parenchymatous cells, there are a number of transition 

 forms, and in many cases it is difficult to say to which form a particular 

 tissue may belong. Such intermediate forms are very frequent in mono- 

 cotyledons in the neighbourhood of vessels ; they are also seen in dico- 



60 



tyledons, as in some of the Cactacece (fig. 59.). As they approach the 

 character of shorter cells, the configuration of the walls, with pores or 

 sharply defined layers, is evident (figs. 60, 61.). 



If we regard the pointing at both ends and the thickness of the de- 

 posit layers as essential characters of liber-cells, then the branched cells 

 discovered by me* in the ovary of some Aroidece (in Monstera and 

 Scindapsus), and in the pith of Rhizophora Mangle (fig. 63.), belong 

 to them. 



Ordinarily the liber-cells are so long, that the whole of them cannot be 

 seen by a strong magnifying power (fig. 62.), and, next to the cells of 

 some species of C/iara and the pollen tubes of some plants, are the longest 

 cells which present themselves in the vegetable kingdom. I have mea- 

 sured liber-cells from 4 to 5" in length, but these are probably not the 



* Wiegmann's Archiv, 1839, vol. i. p. 231.; Schleiden, Botanisehe Beitrage, vol. i. 

 p. 42. 



59 An intermediate form between liber- and parenchyma-cells (a), from the bark of 

 the root of Maxillaria atropurpnrea. 



50 A liber-fibre, short, thick, and porous, from the China regia. 



61 Transverse section of three liber-fibres and some parenchyma-cells from the China 

 regia (Cinchona scrobiculata Humb. Yellow Bark.) The liber-cells show beautifully 

 the deposit-layers and the porous canals. 



52 Upper end of a liber-fibre from the Tilia europcca. 



83 A branched liber-cell from the pith of Rhizophora Mangle. 



