Pethybridgio and Laffeety — Dry-Rot of the Potato Tuber. 215 



decaying tubers themselves. Since, however, as described above, the plants 

 produced from diseased tubers remained healthy, we conclude that the fungus 

 is not capable of attacking the roots. 



Experiments were made to ascertain whether F. cmruleum is capable 

 (like Verticillium albo-atrum) of producing hadromycosis, that is, of growing 

 in and choking up the wood vessels, and thus causing a type of " wilt " 

 disease. 



As a result of several preliminary trials it was found that this fungus 

 refused to grow on freshly cut, living portions of potato stalks, whether 

 inoculated on the freshly-cut surfaces, on the uninjured surface, or even 

 into freshly-made wounds in such stalks. These trials were made with 

 portions of stalks a few centimetres long, from which the leaves were removed, 

 and which were kept moist in test tubes provided with cotton- wool plugs. 



Further trials were next made by inoculating the fungus into rather deep 

 wounds, traversing all the tissues, made in various regions of the stems of 

 leafy stalks cut from the parent plant, and kept with their cut ends in water. 

 By occasionally changing the water and renewing the cut surface at the 

 base of the stalk such leafy shoots, if kept in a good light, will remain in 

 good condition, and continue to grow for some weeks. Uninoculated cut 

 shoots were, of course, also kept under similar conditions for purposes of 

 comparison and control. 



The results of these trials were entirely negative. After four weeks the 

 inoculated stalks showed no signs of wilting, and microscopical examination 

 of the tissues showed that there had been no extension of the fungus 

 from the inoculation wound either in the cavities of the wood-vessels or 

 elsewhere. 



The inoculation of plants growing in pots was then proceeded with, three 

 series of experiments being made. In the first series the stalks, when about 

 twenty centimetres high, were inoculated (under as aseptic conditions as 

 possible) just below soil level, the wound being made at a node. After 

 inoculation the wounds were bound up with tinfoil, and the disturbed soil 

 replaced. Inoculation with Verticillium albo-atrum in this manner in- 

 variably results in causing a wilt disease of the plant, but in no case did this 

 happen with F. cceruleum. 



One of the six inoculated plants did, it is true, die prematurely, but this, 

 it is believed, was due to the effects of a somewhat drastic fumigation 

 rendered necessary by an attack of aphides from which both the inoculated 

 and control plants temporarily suffered. The dead plant was thoroughly 

 examined microscopically, but no mycelium was found in the stem except at 

 the inoculation wound from which no spread had occurred. The same was 



