POTATO -PTJNCftJS. 119 



question before ns, but I would only remark, in reference to the 

 Pyth'kim. that it is a species which has not hitherto been descrilied, 

 and which I now call P. vexans, because it has occupied me for aliuosl, 

 the whole of two long years. 



Before entirely leaving this department of the subject, I wish to 

 record another experiment ; and in this case also, not because I gained 

 anything positive toward the solution of our problem, but because it 

 shows how carefully one must guard against being deceived in investi- 

 gations of this kind. For the sowing of Pythium vexans I had 

 got, beside others (July 20), half-a-dozen fresh new Potatoes, Ex- 

 ternally they looked liealthy. One was immediately used for experi- 

 ment and cut in two. I placed a sowing of Pythmm on the cut 

 surface of the one half; I did not inoculate the other half; each was 

 placed sepai-ately under a small glass bell in a moist atmosphere. On 

 the next and the second day the germination of ihePythium, as described 

 above, was confirmed in the inoculated half. But on the third or 

 fourth day I was agreeably surprised to find on the inoculated surface 

 the beautiful conidiophores of the Potato-fungus. 



It is true that they were not growing on the very spot where I 

 had sown the Pythhcin vexans; still, they were close to it. From that 

 point outward to the edge they covered the surface of the section, and 

 they also extended down the thin skin of the external surface for 

 some distance. In these places mycelium was always found in the 

 interior of the tubers. Search was made in vain for a connection 

 between it and the young plants grown from the sowing of the 

 Pythium. The non-infected half, which from the beginning of the 

 experiment had been kept quite isolated, also presented, ou the same 

 day as the infected half, conidiophores of the Potato-fungus on its 

 surface. Up to this point the other Potatoes had been preserved in a 

 different place, lying exposed to the dry air of the room. Externally 

 they appeared to be he'althy, with the exception of one or two dark 

 spots on the surface. They were placed without any artificial in- 

 fection under glass bells in a moist atmosphere, and the disease, to- 

 gether with the eruption of conidia, appeared in all of them in from 

 two to three days. I had, therefore, been working with material 

 which was diseased before I employed it in the experiment ; and this 

 need not seem strange when we remember that from the middle of 

 July onwards the Potato-fields of this district had been frightfully 

 destroyed by Phyto'phthora. Still, the appearance of the conidiophores 

 of the Potato-fungus on the half of the Potato infected with Pythium 

 might have led to a serious and disagreeable deception, but for the 

 opportunity of checking it just described. 



7. In the tissues of Potatoes penetrated with the mycelium of 

 Phytophthora, there sometimes appear other bodies, which might be 

 regarded as oogonia or oospores of the Potato-fungus. I have several 

 times found them with Pythium vexmis in old collapsed tubers which 

 had sprouted in the ground, and once without Pythium in a living 

 stalk which had been on the ground. But they were always restricted 

 to those regions which were occupied by the Phytophthora mycelium, 

 and always occurred (with one doubtful exception) in the interior of 

 the dead cells of the Potato. These bodies, when ripe (see fig. 7), 

 have a globular form with a fine muricated surface. The prominences 



