VISIBLE CONSTRUCTIVE ACTIVITY IN PROTOPLASM. 579 



as in Selaginella (belongiug to tho t'auiily of the Lycopoiliiiere). Hero wo have 

 inclineJ walls formed alternately on tiie right aiul left, and thus arise two rows of 

 segment-cells, arranged with regard to the axis of growth like the Ijarbs of a 

 feather on their axis. The base of the apical-cell is three-sided in the stems of 

 horse-tails, most ferns, and mosses. Such an apical-cell may be best compared to 

 a three-sided pyramid, whose sides are not flat but somewhat convex. The side of 

 this cell, which corresponds to the base of the pyramid, forms the free end which is 

 not bordered by other cells, but by the air, or earth, or water; the three other .sides, 

 directed towards the base of the growing plant-organ, converge at a point which 

 lies in the axis of growth of the organ. The insertion of division-walls occurs 

 parallel to these three slightly arched sides, and in a regular succession, so that the 

 segments cut off appear arranged like the steps of a spiral staircase. The walls 

 which are afterwards inserted in the segment-cells are partly parallel, partly 

 at right angles to the first-formed walls. On the whole it cannot be questioned 

 that in this building, as in the buildings of men, the walls are intercalated at right 

 angles to one another in three dimensions of space. 



In the root-tips of ferns and horse-tails, we also have a three-sided, pyramidal 

 apical-cell, as just described, but the construction is to some extent complicated 

 by the fact that division-walls also arise parallel to that side which corresponds to 

 the bixse of the thi-ee- sided pyramid. The segments so cut off, which divide 

 up again into many cells by radial walls, cover the apical-cell like a cap. This 

 structure, which has been called the root-cap, serves to protect the apical-cell at 

 the root-tip as it pushes its way into the earth, and would otherwise be exposed to 

 many dangers. 



In some ferns, and in most flowering plants, two, or even a group of cells are 

 to be found at the tips of the growing stems. Some trouble has been taken to 

 reduce the arrangement of these to three types, but it does not lie within the scope 

 of this work to describe these in detail. That the construction in these cases is 

 extremely complicated, that in many cases it is very difficult, frequently even 

 impossible, to follow and to establish with certainty the plastic processes, does not 

 in the least alter our conviction that the construction of the growing organs in 

 these plants is accomplished according to rule, and that a definite plan underlies 

 the form of every species, which is indicated beforehand by the specific constitution 

 of the protoplasm. 



It must also be here remarked, to prevent misunderstanding, that in plants in 

 which numerous organs are developed with various functions, all the growing 

 parts are not formed in the same manner. This, however, is not opposed to the 

 fact that in each species the same constructive plan is invariably adhered to. The 

 directions of the .septa inserted in the growing rhizoids, leaflets, and capsules of 

 a species of moss may differ much among themselves, but in each species they 

 are always the same in the vai-ious organs. In flowering plants, too, the processes 

 in the formation of the root-cap, the stomata, the pollen-grains, and so forth, vary 

 very much among themselves, but these processes are retained in each species of 



