32 STRUCTURE AND GROWTH 
formation of the cell, but in a much lower proportion. It is 
subsequently absorbed ; frequently, however, not before ossifi- 
cation. This is precisely what occurs in vegetables. The walls 
of the cartilage-cells become thickened (compare figs. 6 and 7 
with fig. 5), which is also the case with many vegetable-cells. 
No distinction, however, between primary cell-membrane and 
secondary deposit can be observed in cartilage-cells, and such a 
deposition in strata as is often distinctly seen in thickened cells 
of plants cannot be made out here with sufficient certainty. 
The cell-nucleus in the meantime, when not absorbed, remains 
lying upon the inside of the thickened wall. An instance of 
actual thickening of the cell-membrane without a stratified 
deposit, does not, however, appear to be wanting in plants, 
e.g. the pollen-tube of Phormium tenax. (See the Introduction.) 
But it seems, that a thickening of the walls of the cartilage- 
cells does not take place universally, it does not for instance in 
the ossifying cartilages; the true cartilage substance may also 
be formed entirely, or at least chiefly of the intercellular sub- 
stance. The condensed cell-walls subsequently coalesce with 
one another, or with the intercellular substance, so that at last 
only the cell-cavities remain in an homogeneous substance. 
Whether the walls of those cartilage-cells which do not undergo 
any thickening become blended with the intercellular substance 
or not, remains uncertain. An analogous instance of coalescenec 
of the cell-walls is afforded by vegetables, for Schleiden has ob- 
served such a blending in the layer of bark which lies im- 
mediately beneath the cuticle of the Cacti. 
The cartilage-cells often contain either simple nuclei (i. e. 
without cells around them), or young cells with such nuclei. 
These young cells are formed free within the parent-cell, 
without vascular connexion. Their nucleus is first formed, and 
afterwards the cell around it, just as in the true cartilage-cell. 
This is one of the most important instances of accordance be- 
tween animal and vegetable cells, for the latter, according to 
Schleiden, are developed in like manner from the nucleus, and 
likewise within a parent-cell. (See the Introduction.) We may 
therefore confidently compare the nucleus of these young cells, 
as also that of the true cartilage-cell, to the cytoblast of vege- 
table cells. Their shape and the eccentric position of their 
nucleus, placed as it is upon the internal surface of the cell-wall, 
