872 



or later according to the degree of injury. According to Townsend* the 

 hastening of growth becomes evident in 6 to 24 hours after slight injuries, 

 while severe injuries at first cause an arrestment before the increase in rate 

 begins, which, according to the plant, reaches its maximum in 12 to 96 hours 

 and then gradually returns to the normal condition. Krassnosselsky= traces 

 the increase of respiration to an increase of the respiratory enzyme. He 

 carries out further Kovchoff's experiments which show that an increase in 

 the whole amount of protein and especially of the nucleo-proteids takes 

 place after an injury and then proves (in injured bulbs) that the sap con- 

 tains more oxydases than does that from uninjured specimens. The same 

 is true of potatoes. 



The subsequent reactions of leaves after injury vary greatly according 

 to the species of the plant, the age of the leaf and the time of injury. We 



Fig. 207. Injury to a leaL" of Leucojum vernum, which is being closed l)y callus 

 I'ormation. (Alter Frank.) 



will content ourselves with discussing the two extremes, viz : the reaction of 

 a tough leathery leaf and that of a fleshy one. In the former, Prunus 

 Laurocerasus represents a case in which a sloughing process of the injured 

 cell group is connected with the injury as has already been mentioned under 

 the results of spraying with copper. According to Blackman'' and Matthaei* 

 cither the injured cells alone die, or those immediately adjoining them, 

 according to the part of the leaf injured. A brown zone with a Hghter 

 colored centre is produced around the wound. The epidermis splits in this 

 hyaline region and colorless, very thin-walled, cells grow out of the adjoin- 



1 Townsend, C. D., The correlation of growth under the influence of injuries; cit. 

 Bot. Jahresber. 1897, I, p. 98. 



- Krassno.«selsky, Bildiing der Atmungsenzyme in verletzten Pflanzen. Ber. d. 

 Deutsch. Bot. Ges. 1905, Vol. XXIIT, p. 143. 



3 Ber. d. Deutsch. Bot. Ges. 1903, p. 165. 



4 Blackman, F. F., and Matthaei, G. L., On the reaction of leaves to traumatic 

 stimulation. Ann. Bot. XV; cit. Zeitschr. f. Pflanzenkrankh. 1902, p. 61. 



