i8a THE POPULAR SCIENCE MONTHLY. 



ing itself up more closely and thickly, a few doors and windows are 

 still left open in it, through which communication may still take place 

 with the adjoining cells ; this occurs by the cell-wall not becoming 

 strengthened at particular points ; and when, in the course of time, the 

 shell has become still thicker, these places appear as pores or canals, 

 which lead outwardly from the interior of the cell. And it is worthy 

 of remark that at each point where such a canal penetrates the thick- 

 ened cell- wall a corresponding passage is also left open in the next cell, 

 so that the two canals meet each other, and are only sej)arated by a 

 thin partition. Communication continues uninterrupted by these pore- 

 canals. 



The plant-cell is, nevertheless, subject to the fate of all life 

 it grows old and dies at last. It seldom survives a summer ; toward 

 the end of the fall its activity becomes weaker. Dissolution gradu- 

 ally overcomes the dead protoplasmic bodies, and only the empty cell- 

 wall is left, which may continue to exist as a vacant chamber for years 

 and centuries after the living nucleus has perished. As a rule, the cell 

 propagates itself before it dies ; as an earth-worm may be divided into 

 two parts, each of which will become an independent individual, so 

 the parent-cell divides itself into two daughter-cells, which supply the 

 place of the mother, and continue their life-activity with renewed 

 vigor. 



II. 



Such in its principal features is the economy of the plant-cell. It 

 is fed by the absorption of fluid and gaseous foods ; it elaborates those 

 foods into the most diversified products ; it respires ; it strengthens 

 and thickens its shell, yet in such a manner that it can continue in liv- 

 ing intercourse with its neighbors ; it propagates itself by splitting 

 into daughter-cells ; it grows old and dies. Let us now glance at the 

 arrangements and laws according to which the cells act in organic con- 

 nection as citizens of a single state. As there are wild bees that do 

 not live together in a hive, as there are human tribes that wander 

 around in the woods without organic connection, so there are plant- 

 cells that remain isolated during all their lives ; they all perform in 

 the same manner the business of their whole existence, which is highly 

 primitive, and unadapted to perfection ; their progeny does not con- 

 tinue in social connection, but separates into wholly free individuals. 

 Such plants, which always consist of single cells, are called one-celled ; 

 they are found among the lowest forms of the microscopic world, 

 among the algae and the fungoids. The green coating that covers the 

 rocks, the tree-trunks, and the shingles of the roof, is resolved by the 

 microscope into innumerable green round cells ; the brown scum that 

 floats upon ponds and ditches exposed to the sun, the yeast-plant, the 

 bacteria that produce putrefaction, are one-celled plants of this kind. 



Generally, however, the plant-cell is, like man, a social being, which 

 finds its true calling only in state-life. In most growths, from that of 



