THE COMMON WALL OF ADJACENT CELLS. 



ITI 



Nehemiah Grew (1682), believed that he had discovered that the cell-wall frame- 

 work of plants consists of exceedingly fine fibres; and that the cellular structure 

 itself is to be compared to a great number of pieces of Brussels lace arranged 

 upon one another in layers. In this sense he spoke of a cell-tissue {contextus 

 cellulosus) of plants. Although the erroneous character of this view has long been 

 known, the name has still been preserved, and even transferred from vegetable 

 anatomy to animal histology. This need not be wondered at, since a very great 

 number of other scientific terms date likewise from early erroneous conceptions. 



I shall in this lecture only attempt to expound the most general principles 

 of tissue formation; and in doing this, I shall again first deal with the typical 

 forms of tissue, leaving many abnormal tissue structures to be mentioned 

 later. 



As will be remembered from what was said in the last lecture, the cells of 

 a cellular plant arise by the intercalation of new partition-walls in the cell-cavities 

 already existing; and as the cel- 

 lular bodies grow, new partition- 

 walls are repeatedly intercalated in 

 the cell-cavities, in various direc- 

 tions, and in definite order as 

 regards time. It follows im- 

 mediately from this, however, 

 that it is utterly incorrect to re- 

 gard the cells of a growing plant 

 as structures originally free, and 

 only fusing with one another later. 

 This erroneous view, which phy- 

 totomists entertained in earlier 

 decades, must necessarily lead to 

 the fiirther, but also unfounded 



assumption, that the partition-wall between each two neighbouring cells consists from 

 the beginning of two separate lamellae ; and accordingly a cement was further believed 

 to be necessary, by means of which these wall-lamellse of neighbouring cells were 

 stuck fast together. This cement was called the intercellular substance. The organ- 

 isation of the partition-walls, especially in cells with thick walls, appeared thoroughly 

 to confirm this view. This has long been given up, however, since we now know 

 that each new partition-wall between two neighbouring cells of a tissue appears 

 as an immeasurably thin solid membrane ; and that, from the mode of origin of 

 the latter, as described previously, not the remotest reason exists for considering this 

 membrane — the new partition-wall — as consisting of two lamellae. If later on, with 

 progressive growth of the tissue-cells, the thickened partition-wall nevertheless 

 presents itself as a double lamella, or as already mentioned becomes split into two 

 lamellae so that spaces arise between the cell-chambers, this is simply due to 

 a subsequent splitting of the originally simple partition-wall into two lamellae, and 

 is not a proof that the partition-wall was composed, in the first instance, of two 

 such lamellae. 



If the partition-walls between neighbouring cells attain a considerable thickness 



Fig. 109. — Transverse section through the soft parenchyma of the stem 

 oi Zea Mays, gw partition wall common to each of the two cells; sinter- 

 cellular spaces produced by the splitting of this wall. 



