FORCES. 



169 



epidermis of the Spiderwort and place it under the micro- 

 scope (Fig. 242) we shall see the protoplasm at work, going 

 round and round each cell with a motion as vital as that in 

 our own blood. This rotary motion is called Oyclosis, or 

 Intercellular Oirculat'wn, because it is restricted to the cell, 

 and also to distinguish it 

 from sap circulation, 

 which is ostensibly car- 

 ried on by physical force 

 alone. Yet the proto- 

 plasm guides and controls 

 every movement, whether 

 physical or chemical, with 

 the skill of a master- 

 builder. It not only 

 creates, but sends to 

 every part the needed 

 materials and arranges 

 them in their places. It 

 carves the form of each 

 leaf; it moulds the pollen- 

 grains in the cells of the 

 pollen-mothers; it makes 

 the flower-palace for the 

 pistil ; it engenders the 

 embryo which is to con- 

 tinue the family line. 



415. Special Movements of 

 the plant as an individual. — 

 If a Morning-Glory seed be 

 planted with its radicle upper- 

 most, in a dark cellar, where 

 no light can possibly reach it, 

 the radicle will twist about 

 until it regains its true posi- of the drcaiation, 

 tion. The caulicle and plu- 

 mule will do the same, curving upward ; then, when light is admitted, 

 they will bend towards it by contracting the cells on the illuminated 

 side. This contraction is not the result of growth ; it is independent 

 of growth ; for if we split the stem vertically, the illuminated side 

 curves still more, while the shaded side straightens j proving that the 

 light, though a strong agent, is not the only force at work, and that 

 this movement is directed by a vitality within. The shoots, as they 

 H 15 



KiG- 242. — Bit of epidermis from the calyx of 

 Spiderwort {Tradescanlia virginica) : e, e, epider- 

 mis with small cells, one of them with a stoma, 

 8; p, & long, jointed hair, each joint a cell ; ii, 

 nucleus. The arrows indicate the direction 



