25 



within the cyst or sporangium. In Fuligo the sporangia 

 are not separated but combined together (an aethalium). 

 In other instances the sporangia are separated and raised 

 off on stalks. The wall of the sporangium becomes friable 

 and breaks down, and the spores, lightly hanging on the s 

 capillitium threads, are scattered around. The spores 

 germinate in moisture, their coats rupture and they come 

 out. They are at first amoeboid, but soon become pear- 

 shaped (swarm-spores or flagellulae), with a fine whip-like 

 flagellum at the narrow end. They are active for a time ; 

 then, withdrawing their flagella, they become rounded 

 and undergo division by karyokinesis. There may be several 

 successive generations, but ultimately they become amce- 

 bulae which exhibit mutual attraction. A few come to- 

 gether and coalesce, others draw near and "join up," 

 and in this way the composite mass, the plasmodium, is 

 formed. 





 Briefly describe the Structure of the Plasmodium in the 



Mycetozoa. 



The peripheral portion is firmer and clearer than the 

 inner mass, which is very granular and traversed by branch- 

 ing vein-like thickenings, within which there is a constant 

 streaming of the protoplasm. Some species (e.g., Fuligo) 

 have granules of lime. There are numerous nuclei, and 

 contractile vacuoles are seen near the periphery. The 

 plasmodium creeps by outpushings of the protoplasm 

 (pseudopodia). 



To which Class of Protozoa does Plasmodiophora brassicse 

 belong ? 8tate its Importance, and briefly describe 

 its Life-history. 



To the primitive Class, Proteomyxa. It causes a disease, 

 called " Fingers and Toes," or " Club-root," in turnips, 

 cabbages, etc. In the root cells the plasmodium is seen 

 as " a yellow stringy slime." Its nuclei break up, are 

 reconstituted, then divide by karyokinesis, and numerous 

 gametes are formed. These conjugate in pairs and form 

 zygotes which give rise to spores. When the roots of the 



