STUDIES ON CLUBROOT OF CRUCIFEROUS PLANTS 431 



which is the same time that under the most favorable circumstances it 

 takes swarm-spores to pass thru the root hairs into the cortical tissue 

 and to develop sufficient hypertrophy to be visible to the naked eye. 

 Kleimenov (1912) tried the same experiment and failed. In the writer's 

 experiments it was also tried repeatedly, always with failure. If the cul- 

 tures were kept free from bacteria the root underwent no change. If 

 bacteria were added, the root became soft and foul-smelling, whether the 

 test tubes were closed with cotton plugs or sealed with paraffin over 

 cork or cotton stoppers. Sealing did not stop the growth of the bacteria, 

 as Pinoy claims for his experiments. 



Altho authors popularly describe with some assurance various ways 

 in which the organism may enter the host, no one has observed the real 

 process. Even Woronin, who believed that the organism passes thru the 

 root hair, was never able to demonstrate this clearly. Nevertheless he 

 felt assured that it enters in the form of a uninucleate amoeba, and his 

 ODinion has been accepted by most investigators. A few workers, such as 

 Worthington G. Smith (1884), maintain that the organism enters the 

 root in the form of a plasmodium, but this theory has never been accepted 

 generally. The question was revived again when Kunkel (1915) studied 

 the powdery scab of potato, in which the swarm-spores are found to fuse 

 before attacking the host. 



There seems to be no doubt in the minds of Maire and Tison (1911) 

 and Schwartz (1914) that all the other known parasitic myxomycetes 

 enter immediately after the swarm-spore stage. This conclusion is based 

 on the fact that many of the slides of these investigators show the uninu- 

 cleate forms in the apical cells. There is no other theory that would explain 

 this phenomenon, unless a single uninucleate amoeba of an infecting 

 plasmodium passes thru the intervening cell walls and spreads in this 

 manner thru the tissue. This is improbable. 



Because of the diminutive size of the swarm-spore, the only satisfactory 

 method for studying penetration appears to be by means of stained sec- 

 tions of roots showing the earliest stages possible. In the first part of this 

 work, young plants from the greenhouse were used, but none of the stages 

 were young enough to give just what was desired. An attempt was then 

 made to grow plants in large test tubes on screens so arranged that the 

 roots were hanging in muck-soil filtrate containing a heavy suspension of 

 spores. The roots did not develop well when immersed in the liquid 

 medium, and but few root hairs were present. An attempt was then made 

 to grow seedlings in soil, in flats six inches square, with diseased tissue so 

 plentiful that none of the plants could escape infection. The roots were 

 fixed and embedded at intervals before the time when ordinary symptoms 

 became apparent to the naked eye. This gave nearly all the early stages 



