534 FETCH : 



The dimensions of the macroconidia vary enormously. 

 17 X 10 [X is a common size, and so is 12 x 8 \k. But many 

 are only 8x5 [x, or 9x7^; while, on the other hand, some 

 attain 19-30 x 11-18 [k. When mature, they are greenish- 

 black or brownish- black. In general, they are oval, truncate 

 when they remain united ; but sometimes they are pyriform, 

 and the apical spore may be spherical. Howard states (10) 

 that the colour is contained in the cell contents, not in the 

 wall ; but it is evident when they germinate that the wall is 

 coloured and the contents hyahne. 



There is no doubt that the macroconidia are formed by the 

 extrusion of masses of protoplasm. When the chain of 

 conidia is fully formed, it frequently remains in contact 

 with the apex of the conidiophore, and as the latter is then 

 practically not inflated at the top, the conidia appear to be 

 ordinary acrogenous conidia. But if the process of formation 

 is watched, their production from within the conidiophore is 

 unmistakable. Sometimes the last-formed conidium of a 

 chain fails to be pushed completely out of the tube ; in that 

 case, the extruded portion becomes oval, wliile the part 

 still in the tube remains cyhndric, and the conidium 

 acquires its spore wall and blackens while retaining this 

 shape. The occurrence of such spores, socketed in the tube, 

 confirms the previous observations as to the mode of 

 production. 



Massee has stated (6) that by staining with chlor-zinc-iodide 

 he was able to determine that the wall of the developing spore 

 first began to be formed at the distal end, and thinned away 

 along the sides. T have not been able to stain the wall with 

 this re-agent. 



The macroconidia do not germinate in water. When sown 

 in a nutrient solution they germinate in about five hours. 

 Cobb's statement that they require a period of rest before 

 germination is not correct. 



In flask cultures, the conidia ultimately form a black 

 powdery mass on the surface of the hquid. 



As Howard (10) has previously shown, it is not necessary 

 for the formation of macroconidia that the cultures should be 

 kept in the dark. 



J 



