INJURIES INDUCED BY PLANTS 51 



tissues without producing any appreciable effect on them. 

 Especially is this the case when the cells have already attained 

 the condition of permanent tissue before the mycelium has 

 appeared in or between them. 



The mycelium of Calyptospora has no apparent action on the 

 permanent tissues of Vaccinium Vitis-Idcea ; whereas, in very 

 young shoots, it causes enlargement of the parenchymatous cells 

 of the cortex, with the result that very remarkable swellings are 

 produced on the stem. 



One of the most frequent results of the action of fungi is that 

 a stimulus is given to cell-division. Mention may be made of 

 the swellings on the stems of silver firs whose cortical tissues are 

 infested by ALcidium elatinum, of the swellings on the stems of 

 junipers owing to Gymno sporangium, &c. Still more frequently 

 the infested parts are stimulated to display altogether abnormal 

 growth. Flowers, fruits, and portions of stem of various species 

 of plants are transformed in a most peculiar manner by fungi 

 belonging to the genus Exoascus. It does not necessarily follow, 

 however, that their vitality is thereby prejudicially interfered 

 with (e.g. witches' brooms of the hornbeam, &c.) 



Changes in the cell-contents are often noticed which are 

 indirectly induced by fungi. This is the case, for instance 

 when the mycelium of Hysterium macrosporum kills the elements 

 of the bast at the base of spruce-leaves, thereby destroying 

 their capacity of conducting plastic materials, while the other 

 parts of the leaves still live and assimilate. The result is that on 

 account of the newly formed carbo-hydrates not being able to 

 get away from the leaf, all the cells become packed full of starch. 



The tannin which is dissolved in the cell-sap offers excellent 

 food for the mycelium of Polyporus igniarius, being absorbed first 

 of all by the hyphae which penetrate the sound oak-wood, after 

 which it undergoes metabolic changes in the youngest parts of 

 the mycelium. The occurrence of mycelia in oak-timber is there- 

 fore followed by the disappearance of tannin, the smell of which 

 has long been regarded by practical men as a proof of the sound 

 condition of the wood. The conversion of a portion of the cell- 

 contents or of the cell-walls into turpentine under the action of 

 the hyphae of Peridermium Pini is also interesting. Although 

 it often happens that the starch-grains disappear very soon from 



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