THE DEPOSIT LAYERS OF THE CELL-WALL. 79 



greater or less number of astathe layers, which swell up 

 strongly in sulphuric acid. (Bot. Zeit. 1854, p. 51, Tab. 1, 

 fig. f6-17, a, h). 



The youngest of the secondary cells, both of the wood and 

 of the alburnum, exhibit no difference; they correspond in 

 size, form, and structure not only with each other, but also 

 with the two parent-cells, with which they constitute the 

 compound layer designated the ' cambium.' The first appa- 

 rent distinction in the structure of the secondary cells destined 

 for the ligneous substance, and of those belonging to the 

 alburnum, is shown in the dotting — the dots in the former 

 being always distinct, and in the latter always grouped in a 

 cribi-iform fashion. (Bot. Zeit. 1854, Tab. 1, fig. 24). 



In the part of the ray belonging to the ligneous substance 

 it is the cell-fibres and lamellar-fibres, and in that belonging 

 to the alburnum substance it is the telial-fibres which retain 

 unaltered the cambial condition of their walls ; no further 

 thickening of the wall ever takes place in these cells. In the 

 ligneous part of the ray it is the woody fibres, and in that part 

 which belongs to the alburnum it is the true alburnum-fibres 

 which exhibit a further thickening of the cell-wall, which is 

 effected by the deposition of new layers on the inner side of 

 the cambial-wall. These layers of the second and subsequent 

 generations afterwards constitute by far the main part of the 

 thickness of the wall, whilst the cambial-wall contracts to 

 such an extent, that its original constitution of cell-membranes 

 and deposit-layers, which in the course of its development was 

 distinctly demonstrable, is no longer perceptible. In this con- 

 dition I have myself, he says, several times confounded the 

 cambial-wall with what, in other situations, I have correctly 

 described as 'eustathe' (intercellular substance, but not in the 

 sense in which Mohl understands that term), or as ' cell-glue.' 

 Thus, for instance, in my Leben d. Pfianzenzelle, t. ii., fig. 

 27 e, it is not ' eustathe,' but the cambial-wall, contracted by 

 sulphuric acid and no longer capable of expansion, that is re- 

 presented. 



In a former memoir " Upon the formation of the deposit 

 layers," I have shown how these additional layers arise from 

 the regeneration of the ptychode-sac. 



The additional layers of the second and subsequent genera- 

 tions, both in the ligneous and in the alburnum fibres, in their 

 youngest condition, assume a beautiful rose-red colour when 

 brought into contact for some hours with dilute sulphuric 

 acid. In the same section and under precisely similar influ- 

 ence of the acid the cambial-wall remains unchanged, both in 

 the region of the ligneous and of the alburnum-fibres, as well 



