The Fungus Pests of Garden Plants 



cruciferous plants, many cruciferous weeds, including Charlock and 

 Shepherd's Purse, are attacked by this pest. The protoplasm of 

 the fungus ramifies amongst and within the tissues of the roots of 

 the plants attacked, and ultimately produces an abundance of spores 

 so small that more than thirty millions would be required to cover 

 a superficial inch. Whether the Turnip is first in a bad condition 

 of health and is then easily attacked by the fungus, or whether the 

 fungus makes its attack upon perfectly healthy plants, is perhaps an 

 open question, but, as a rule, unhealthy and weakly plants are the 

 earliest to fall. The Plasmodiophora belongs to the Myxomycetes, or 

 'slime-fungi,' which, as a rule, live upon decaying vegetable material. 

 Very young seedlings, if isolated, and treated with water in which the 

 tissue of old Finger-and-toe has 

 been macerated, are soon at- 

 tacked, and the disease arrests 

 growth. The spores are capable 

 of resting in a state of vitality for 

 a long time, and can easily with- 

 stand the frosts of winter. The 

 illustration shows at A the fungus 

 in its protoplasmic condition, and 

 at B its ultimate sporiferous or 

 ' seed '-producing stage, when the 

 protoplasm has changed to a mass 

 of minute spores (enlarged five 

 hundred and twenty diameters). 

 When a spore in due course 

 germinates, its protoplasmic con- 

 tents escape through a small aperture in its wall and begin moving 

 about of their own accord in a slow writhing manner. The move- 

 ment is so much like that of the microscopic animal organism found in 

 ponds, and called Amoeba, that this tiny mass of moving protoplasm is 

 called Myxamceba, to denote that it is an amoeba-like form produced by 

 one of the Myxomycetes. Each myxamceba is drawn out at one spot 

 into a fine delicate tail or cilium, as at C, D, E, and is capable of a 

 creeping motion in moisture. When quite free from the spores, trans- 

 parent expansions or limbs extend from the bodies of the myxamoebae, 

 as at F, G, and when these organisms, after existing in the soil 

 for a longer or shorter time, reach the roots of cruciferous plants, 

 which they apparently enter through the root-hairs, they again assume 

 the protoplasmic condition shown at A, and live within the cells, at 



419 E E 2 



X-320. 



FUNGUS OF FINGER-AND-TOE DISEASE 

 Plasniodiophora brassier 



