356 GENERAL PLANT PATHOLOGY 



restitution, viz., that of the cell and that of the tissues. The experi- 

 ments of Tittman have shown that the waxy cuticle of the castor-oil 

 plant, Ricinus communis, may be restored after removal. Exposure 

 of the protoplast results in many cases in the formation of a new cell 

 membrane, as is illustrated in some of the large-celled algae belonging to 

 the Siphoned. Frequently, it is possible to demonstrate the restitu- 

 tion of the cell membrane by the process of plasmolysis in which the 

 protoplasm is made to retreat from the cell wall. The time varies for 

 its formation under conditions of plasmolysis. In Conferva, it takes 

 place in one to two days, in Zygnema in three to four days. When the 

 root hairs of dicotyledonous plants are plasmolyzed new membranes 

 are formed about the protoplast. 



Wounded siphonaceous algal cells {Caulerpa, Valonia, Vaucheria), 

 where the cell wall has been injured, are capable of restoring the cell 

 wall. Some fungi show such restitution also, while the injured cells 

 of the higher plants lack this power. A few exceptions are known where 

 nettle hairs of Urtica dioica may imperfectly replace the broken-off tip. 

 Pricking the turgid cell of Valonia utricularis, as I have done with 

 fresh specimens in Bermuda, is followed by the escape of a liquid jet 

 and later the opening is closed by a gall-like, protoplasmic, chloro- 

 phylless plug. 



It has been demonstrated that the important cell wall can be regen- 

 erated on fragments of protoplasm provided the influence of the nucleus 

 is felt in such formation. Klebs has shown that, with the removal of 

 the nucleus from the cell, that cell has lost all its power to produce new 

 cell walls, but a distant nucleus may extend its wall-forming influence, 

 when removed several millimeters away in an adjoining cell. 



In the restitution of tissues, we will consider those cases in which the 

 injured cells remain unhealed, but in which the uninjured neighboring 

 cells bring about the restitution. The removal of the rhizoidal hairs 

 on the thallus of Marchantia is followed by the appearance of other 

 hairs in a few days, which may grow out through the cavity of the 

 mutilated one as described so carefully by King. The mutilated 

 tip, or growing point, of many multicellular algae is replaced by the 

 development of the uppermost intact cell. Brefeld found in the 

 sclerotia of Coprinus stercorarius the inner cells are able to regenerate 

 the outer black cuticularized coat, if that is removed. 



The number of cases of tissue restitution known in the higher plants 



