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, 



