

ANATOliy AND PHYSIOLOGY OF 



Fig 1\ 





may be more or le&s perfectly drawn out into a spirally wound 

 band. This plienoracnon, together mth the visible conditions of 

 structure, to be spoken of directly ^ appear to me to indicate that 

 the secondary cell-membranes, without being composed of actual 

 piimitive fibies (which cannot in any way be demonstrated), pos- 

 sess indeed a fibrous structure, since their molecules are connected 

 moie firmly in the diiection of a spiral than in any other direc- 

 tion. f^See '^On the Structivre of Vegetable Meonbrane/' in my 

 " Vermischte Schriften" ) 



Next to these cells, appearing perfectly homogeneous to the ej^e, 

 come such as exhibit a very tine spiral streakmg of theu* mem- 

 brane, as is the case in the cells of many woods, e,g ^in Piiiiis syl~ 

 "vestriSy and in a very striking degree in the bast-tubes of the Apo- 



cynese and Asclepiadese, e.ty, in Vinea 

 (fig. 17), ^er um^ Geropegia^^iidHoya 

 Although in many of these cases also the 

 membu^ne has thLspect of being com- 

 posed of separate fibres lying very close 

 together, yet this appears actually not 

 to be the fact, but the streaking to be 

 dependant upon the unequal thickness 

 or density of the differ en ij paits of a 

 B A piece of the same, Connected membrane. In favour of this 

 aiorehi^^iiiy maguifita -^^ -^ particular, the circumstance, that 



in the blst-fibres of the Apocj/uege, the spiral is v^ound 

 sometimes to the right, sometimes to the left, in the 

 superincumbent layers of the same membrane; the ap- 

 parent fibres, therefore, then cross, a condition of which 

 I know no example in the actual division of the se- 

 condary membrane into fibres. 



In other cases occur, instead of the streaks, perfect 

 slits running in a spiral direction, by which the second- 

 ary layers become divided into broader or narrower 

 A Liber coll of bands (fibres), running parallel with each other. The 

 vuLca major, ^j.^qqj^iqji of ^i^q Spiral in which the fibres run is, as a 



rule, the same in all the cells of a tissue ; theiefore the fibres of 

 two contiguous cells cross upon their two coherent walls. In the 

 overwhelming majority of cases the fibres are wound to the right 

 (in a botanical sense, i e., therefore in the manner of a left-handed 

 screw). Instances of the contraiy do certainly occur, sometimes 

 merely as isolated cases in particular elementary organs, some- 

 times regularly in particular specimens of a plant. Such spiral 

 fibres occur in rarer cases in the common parenchymatous cells of 

 the stem and leaf-stalk ; for example, to a very remarkable extent 

 in various species of Nepenthes, in many Orchidese ; on the other 

 hand, they are more frequently confined to special organs, for in- 

 stance to the elaters of the Hepaticse, the cells of the sporangium 

 in Equisetimi (fig. 18), a portion of the cells of the leaf and the 



