118 Fungi, Bacteria und Pathologie. 



and also that species o{ plants „immune" in nature can be artificially 

 rendered susceptible. 



Further experiments showed that the conidia oi the fungus 

 produced on a „cut" leai are able at once to infect f u 1 ly 

 uninjured leaves of the same host species. 



In other experiments, a method suggested by Prof. H. Marshai 

 Ward, with the object of avoiding lesion of the leaf, was adopted. 

 Leaves were injured by touching the upper epidermis for a few seconds 

 with a red-hot knife, and conidia were sown on the injured place. It was 

 found that the cells immediately surrounding the place of injury were 

 rendered susceptible to the attacks of a „biologic form" which is unable 

 to attack uninjured leaves of the plant in question. 



In the third part of the paper, dealing with general considerations, 

 the following hypothesis is advanced as to the actual manner in which 

 the injury to a leaf causes it to become susceptible to a „biologic form" 

 otherwise unable to infect it. It is supposed that the leaf cells of each 

 species of host-plant contain a substance or substances — possibly an 

 enzyme — peculiar to each species which, when the leaf is uninjured and 

 the cells are vigorous, are able to prevent the successful attack of any 

 mildew except the one „biologic form" which has become specialised to 

 overcome the resistance. When the vitality oi the leaf, however, becomes 

 affected by injury, this substance is destroyed, or becomes weakened, in 

 the leaf cells in the neighbourhood of the injury, so that the conidia of 

 other „biologic forms" are now able to infect them. 



The author suggests hat injuries to leaves, caused in nature by hail- 

 storms or wind, attacks of aminals, etc., may produce the same effect as 

 the artificial injuries described above in rendering the injured leaf suscep- 

 tible to a fungus otherwise unable to infect it. Conidia produced on 

 these injured places would be able to infect uninjured leaves, and would 

 spread indefinitely. Such may be the explanation of a common pheno- 

 menon — the sudden appearance of disease caused by parasitic fungi on 

 plants hitherto immune. 



A case is described which, it is believed, gives evidence that the 

 injuries produced by aphides, caused leaves previously „immune" to 

 become susceptible. 



In the concluding remarks reference is made to the antagonisüc 

 forces, concerned in the evolution of a „biologic form", viz., „specialising 

 iactors" and „generalising factors". 



Attention is also drawn to the close parallel between I. the beha- 

 viour of the fungus in the experiments in which the conidia were sown 

 on the tissues of the leai exposed by the cut; and 2. the biological facts 

 obtaining in the class of parasitic fungi known as wound parasites 

 (Nectria, Peziza willkommii, etc.) which are able to infect their hosts 

 only through a wound. A. D. Cotton. 



SCHRENK, H. v., The brown rotdisease ofthe redwood. 



(U. S. Dept. Agric. Bureau of Forestry Bull. XXXVIII. 1903.) 



p. 29—31.) 



The redwood is remarkably free from fungus enemies. In Europe 

 it is attacked by a Botrytis which affects the young branches. So far as 

 is now known the ordinary woodrotting fungi do not attack the wood. 

 There is one disease which does cause some loss however. This is 

 characterised by the oecurrence of many pockets of rotted wood and is 

 known as butt, brown, or pin rot. These pockets ränge in size from 

 tiny specks to several inches in diameter. In later stages the sound 

 wood lying between the pockets becomes rotted almost completely away. 

 This decay Starts in the inner rings of the heartwood and gradually 

 extends outwards throughout the heartwood. It is found only in the 

 okier trees. No fungus has yet been found to be connected with the 

 trouble. Perley Spaulding. 



