Sept. 1894.] 



INJURIOUS INSECTS AND FUNGI. 



59 



reducing substances, whilst the two portions of tissue touching 

 it on either side contain no trace of glucose. The mycelium is, 

 moreover, in no respect the cause of the brown colour, for isolated 

 brown patches of tissue are found in the zone of transition, and 

 these are free from mycelium but already contain bacteria. 

 The latter might, therefore, be regarded as agents of infection. 

 Whether they produce the blackness of the tissue is for the 

 present not yet determined, but it seems to be certain that 

 these dark brown changes precede the invasion of the mycelium, 

 and also that at one point they take their rise from without. 

 For if these apparently isolated dark brown patches which 

 appear in the healthy flesh are cut up into separate layers a 

 region is always found in which the patch extends in a smaller 

 zone towards the exterior. The mycelium also spreads in the 

 same direction. Such spots are not visible from the exterior to 

 the naked eye. 



Whether the mycelium inside the tuber belongs to one or 

 more fungi must be determined later by precise cultural experi- 

 ments. The observations hitherto made have shown in parts, 

 in unusual luxuriance, the colourless randfied growths of coni- 

 diophores which correspond to the " Spicaria Solani." 



On the other hand, as in the case of ordinary " dry rot," my- 

 celium also sprang from the interior towards the exterior in 

 the form of hemispherical, verrucose, white (becoming darker 

 later), hard bundles, distributed in zones. The zone formation 

 in these bundles was produced by spongy layers formed partly 

 of parallel bundles of hyphse, alternating with dense pseudoparen- 

 chymatous layers. In cultivation in a damp environment micro- 

 and macro-conidia of Hypomyces Solani are found later at these 

 parts, which, as is known, are also very frequently found in 

 the ordinary " dry rot." A further remarkable difference in the 

 present case is, however, a still greater irritability of the 

 lenticels, between the elongated cells of which lie numerous 

 colonies of bacteria, which after being a few days in water change 

 into yellowish, thick, slimy layers, consisting of sprouting long 

 and short rods, together with spiral forms and a few cocci. On 

 keeping the diseased tubers in a room, the disease is seen to be 

 inactive, while suberous cells are formed in the zone of transi- 

 tion, and here only is there a disappearance of starch, which is 

 still to be found in abundance in the healthy, and partly also in 

 the older browned flesh. 



From the foregoing observations, it is only possible to throw 

 out conjectures as to the cause of the disease. It may be a case 

 in which the tubers (possibly through defective or excessive 

 manuring) have developed a ferment which gives rise to a de- 

 composition of the contents of the cells, and to the production 

 of matter related perhaps to the humus or ulmic substances. 

 This matter changes, quicker and more intensely in the light 

 than in the dark, into the brown substance which first gives the 

 flesh on the cut surface a rust-red, and later a black appearance. 



