I. RESTITUTIOU OF THE CELL 8 



Plapt cells are not capable of living for a long time in 

 an injured condition. After injury to the cell membrane, or 

 after the mutilation of the protoplast, either the cell is des- 

 troyed, or changes take place in it, which result in a repro- 

 duction of the status quo ante, or of a condition similar to it 

 and of equal value physiologically. These we can designate as 

 healing processes. 



The question as to the restitution of the cell-membrane is 

 of the first importance. On the one hand, experimental inter- 

 ference with the integrity of the cell-wall and its connecbion 

 with the protoplast may be carried out most easily; on the other 

 hand, new cell-membrane formations may usually be proved without 

 difficulty in the object under experimentation. We are thus rela- 

 tively well informed as to the processes of cell-membrane res- 

 titution. 



Various kinds of injury must evidently be considered here. 

 We may remove some layers from the cell -membranes without com- 

 ing in contact with the protoplast itself; we may expose the 

 protoplast by breaking the continuity of its cellulose covering, 

 i. e, by pricking or cutting, or we may loosen the protoplast 

 from its membrane in places, or on all sides, by plasmolysis. 



Because of technique, it will be possible to effect the 

 first kind of injury only in cases of unusually strong cell- 

 walls. That the layers v/hich have been torn off can be replaced, 

 has been proved by Tittman^ with Agave americana . Aloe ligulata 

 and A. sulcata . As is well known, the cuticle on the leaves of 

 these plants is very strongly developed, and may be removed 

 without noticeable damage to the protoplasts. In damp places 

 the newly formed cuticle is weaker than that formed under normal 

 conditions, Tittman observed regeneration of the wax coating on 

 Ricinus communis, Rubus biflorus arid Macleva cor data, Various 

 Sedum and Echeveria species lack this capacity for regenerating 

 wax. 

 (11) Very much greater significance is attached to those cases 

 cin which the protoplast in one way or another is exposed par- 

 tially or on all sides. The effect of injuries of this kind may 

 always be studied experimentally and easily in all cellj. forms 

 and in all plants. The large celled Siphoneae are especially 

 suitable objects for these experiments, but it will be found 

 that in all the principal groups of the plant kingdom, plants 

 are knovm in whose cells healing processes may take place after 

 exposure of the protoplast and new membrane formatiom may be ob- 

 served. In any case, however, the capacity for regenerating the 

 cell-membrane is very much better developed among the lower 

 plants than among the higher ones. 



The experiment, which should throw light upon the conditions 

 of the cell after exposure of the protoplast, is mott successful 

 when it is possible to separate the protoplast partially or en- 

 tirely from its wall, leaving it at the same time unmutilated. 

 Plasmolysis is an excellent condition for obtaining this result. 



Klebs^ has proved that protoplasts can be incited to the 

 formation of new membranes by plasmolytic separation from the 



■^ Beobacht^ ^ber Bj^ldung und Regeneration d. Periderms^ 

 d. Epidermis, des Wachsuberzuges u, d, Cuticula einiger Gewachse. 

 Pringsheim's Jahrb. f, Wiss. Bot. , 1897, Bd. XXX, p. 116. 



p 



Beitr, z, Phya. der Pf lanzenzelle . Untersuch. d. Bot. 

 Inst, Tiibingeii, 1888, Bd. II, p. 489. 



