212 The Scottish Naticralist. 



with granular fungoid matter, and the plant dies. In stronger 

 plants the contest goes on a little longer. The attack is fre- 

 quently made at two or three centres ; and in many cases even 

 upon a slender root, the club is chiefly developed on one side. 

 Where there are lateral roots coming into the tap-root above the 

 clubs, the plant goes on growing for an indefinite length of time, 

 for the matter of the fungus does not appear to be carried by 

 the motion of the sap, but extends by growth from particle to 

 particle. Where the attack is early and of a severe character, 

 the plants are killed when young. Where it is less severe a slow 

 and local process of clubbing goes on during the whole season, 

 and the bulb arrives at fair dimensions. But it is remarkable 

 that, while turnips and cabbages are very often killed outright, 

 charlock and mustard usually go on to flower and seed in de- 

 fiance of considerable clubbing. But in all cases, whenever the 

 plant dies the club ceases to increase in size, and in all proba- 

 bility the fungus, which is the cause of the club, is not the direct 

 cause of the subsequent rotting at all. A club taken and dried 

 will preserve for any length of time. But the clubs are an easy 

 prey to atmospheric disintegration, and to fungi and infusoria 

 which revel in dead matter. 



The evidence seems to me to show that the healthier plants 

 are not the least liable to the attack of this fungus. In going 

 along a drill of turnips in which nearly every plant is afl'ected, 

 there seems nothing to imply that the few which escape were in 

 any respect healthier than the many which are destroyed. Cer- 

 tainly the balance of probability is in favour of regarding the 

 Plasmodiophora brassicce as a pure parasite, demanding a healthy 

 living host for working out its career, from a spore to an amoeba, 

 from an amoeba to a plasmodium, and from a plasmodium back 

 to spores again. I am not perfectly convinced that this is the 

 exact course, but Woronin's conclusions are not to be modified 

 without mature consideration. 



It would thus appear that the turnip husbandry of this country 

 is in presence of a destructive parasite. Hitherto the grower of 

 potatoes has stood helpless before the forests of Pei'onospora i??- 

 fcstajis, with stems small enough to come out in half-dozens from 

 the stoma of a leaf. And here is a fungus of an altogether diff"er- 

 ent and less palpable type, devouring the turnip crop with perfect 

 impunity. Can anything be done to stop its ravages? A re- 

 duction in the frequency of the turnip crop by permitting the de- 

 struction of the germinating power of a greater number of spores, 



