i8 9 5. NOTES AND COMMENTS. 85 



condition is resumed, the organism protecting itself by a new 

 cell-wall. 



The branched filament characteristic of the adult is the result of 

 a unique method of growth. The cell has assumed the resting con- 

 dition, and its protoplasm contracts, leaving the lower end of the cell 

 but remaining attached above. This then is drawn entirely into the 

 upper half of the cell and the empty half becomes shut off by a 

 transverse wall. Similarly a second and a third empty compartment 

 may be shut off immediately above the first. Numerous repetitions 

 of this process occur, and the adult plant is characterised by being 

 composed of a series of empty compartments ending in a true cell. 

 Branching results from a longitudinal but oblique division of the 

 protoplasm into two cells, each of which grows in length, the upper 

 continuing its straight course, the lower being pushed out laterally 

 and thus forming a branch which repeats the mode of growth of the 

 main stem filament. 



The Growth of Wounded Roots. 



In a recent number of Natural Science (vol. vi., p. 9) we 

 referred to some experiments by which Dr. Pfeffer had shown the 

 root-tip to be the seat of sensitiveness to the stimulus of gravity. In 

 the issue of the Annals of Botany, mentioned in the foregoing note, our 

 readers will find an account of some work on the same lines by an 

 American botanist, Professor V. M. Spalding, carried out in Pfeffer's 

 laboratory at Leipzig. The subject is the investigation of the cur- 

 vatures, styled traumatropic, which follow the infliction of wounds on 

 the tip of growing roots. These phenomena were first studied by 

 Charles and Francis Darwin and described in the " Power of Move- 

 ment in Plants." Young seedlings were allowed to grow in moist air,, 

 and a small piece of card was fixed on one side of the tip of the short 

 rootlet by means of shellac dissolved in alcohol. A large proportion 

 of these rootlets became considerably bent, curving away from the side 

 to which the object was attached. A similar result followed when 

 nitrate of silver was used as an irritant, or when thin slices were cut 

 off parallel to one of the sloping sides of the apex. 



In their explanation of these experiments the authors concluded 

 that sensitiveness resided in the tip of the root, a theory which 

 Pfeffer's recent ingenious experiments have put beyond doubt ; and 

 also that extremely slight pressure or simple contact was a sufficient 

 irritant to induce deflection. Detlefsen repeated the Darwins' experi- 

 ments, and came to the conclusion that the curvatures were simply a 

 mechanical result of an injury to the root-cap. When this is injured 

 the tissues beneath are partly released from strain, and extend more 

 rapidly than those on the opposite side, thus causing convexity of the 

 side affected. Professor Spalding, however, observed that curvatures 

 in the radicle of a bean follow a branding of the tip after the removal 



