578 VISIBLE CONSTRUCTIVE ACTIVITY IN PROTOPLASM. 



manner is such as is exliibited by Sarcina ventriculi, a vegetable structure which 

 will be presently treated of in detail. Here the eight daughter-cells produced from 

 one cell appear so connected with one another, that they present, taken together, 

 almost the form of a cube (cf. vol. II. fig. 372^°). One cell always comes to lie 

 in each of the eight corners. Structures of such regularity are of course rare. 

 Usually manifold variations take place. In the so-called poUinia of orchids 

 hundreds of daughter-cells are developed by repeated division, grouped into small 

 balls which again form a large, iri-egular, clumpy mass. It frequently happens 

 that a group of cells, which increases at the periphery in three dimensions of space, 

 in consequence of the intercalation of division-walls, does not exhibit, as would 

 have been expected, a symmetrical growth on all sides, but increases chiefly in one 

 of the three dimensions. This form, which is specially observed in stem structures, 

 depends upon the development of a so-called apical-cell. By this is meant a cell 

 which forms to some extent the apex of a cellular body constructed on a horizontal 

 base. By the insertion of a partition-wall a chamber, a so-called segment, is 

 formed from the lower half of the apical-cell. While fresh divisions are being 

 accomplished in this segment the upper half of the apical-cell again grows up to 

 the original size; and if one did not know that a segment had been cut ofi' from 

 it a short time before, it might be thought unaltered with regard to size, position, 

 and shape. After a little time the segmentation just described is repeated and 

 forthwith it again recovers from the loss, and attains to its original size. Thus the 

 apical-cell cuts off one segment after another at the base, and builds a pedestal on 

 whose highest point it enthrones itself. The apical-ceU comes in this way to be 

 raised always higher and higher, as it were pushing its way through the surround- 

 ing air or water at the head of a group of cells; and to a certain extent the 

 •direction of growth, as well as the internal tissue of the groups of cells cut off from 

 the apex, are ruled and ordered by the processes of division carried on within it. 



This results from the fact that the position of the segments separated from 

 the apical-cell {i.e. of the intercalated separation-walls), is always arranged in a 

 definite manner. If the division-wall, which arises in the lower part of the 

 apical-ceU, parallel to the base and at the same time at right angles to the 

 direction of growth of the cell, and if the further divisions arising in the re- 

 peatedly-divided segments occur in three dimensions of space, as is the case, for 

 example, in the CharaceEe, then the whole plant is built up in stories. The 

 chambers of the lower story are produced from the first segment cut ofi" from the 

 apical-cell, those of the next higher story from the second, and so forth. The 

 whole structure, however, is terminated above by the indefatigable apical-cell, 

 which continues to divide in the same way as at the commencement of the edifice. 



In other cases the separation- walls, which have been intercalated successively in 

 the lower part of the apical cell, take up an essentially difierent position fi-om that 

 in the Characeas. They are frequently placed obliquely to the direction of growth 

 of the shoot-axis, and the base of the cell is either wedge-shaped or three-sided. It 

 is wedge-shaped, for example, in some liverworts (Aneura and Metzgeria) as well 



