xvii.] CLUB-ROOT OF TURNIPS, CABBAGES, ETC. 99 



sometimes wholly filling certain cells, in other instances 

 appearing as strings of slimy protoplasm drawn across 

 from one side to the other. No true mycelial tubes can 

 be seen, and none of the familiar cells so common in most 

 fungi. One fact will strike the observer at once, and that 

 is, the affected cells will be noticed as much larger in size 

 than the ordinary cells of the rootlet in many instances 

 enormously larger. This distention of the cells is a 

 common result of the attacks of parasitic fungi on leaves 

 and roots, and one can understand at once that if each 

 constituent cell of the infant turnip -root or rootlet is 

 distended to ten or one hundred times its normal size, a 

 clublike growth must result. It will be noted too that 

 the cells, though enormously distended, have not burst. 



If a club is examined later in the season say in 

 October a very different appearance is presented, and 

 the change we then see has been gradually going on 

 during the autumn months. The protoplasm of the 

 summer has, by the late autumn, broken up into innu- 

 merable minute spherical portions, and the stringy, slimy 

 mycelium has been replaced by millions of excessively 

 minute spherical spores. These spores may now be dis- 

 tinctly seen to possess a cell wall. The cells of the turnip 

 are now, even more distended than before, and in many 

 instances they will be seen closely packed with the greatest 

 regularity by vast cohorts of the Plasmodiophora spores. 

 It will still be seen that most of the distended cells of 

 the turnip remain intact, and only a few are ruptured. 

 A little pressure of the covering glass of the microscopic 

 slide will, however, speedily break some of the cell walls, 

 and the spores will pour in enormous quantities through 

 the breach into the surrounding film of water. This 

 condition of the disease is illustrated at Fig. 37, enlarged 

 200 diameters, where the spores are seen pouring out 

 through the breaches in the cell walls. The spores are 

 farther enlarged to 1000 diameters at Fig. 38, so that 

 their size may be compared with other spores drawn to 



