120 Mortier F. Barrus 



Gardner (1918:21), in his spore-germination studies of Colletotrichum 

 lagenarium, concludes that a rather abundant supply of oxygen and 

 a contact stimulus is necessary for appressorium formation, and that the 

 presence of food material does not seem to inhibit such formation. Dey 

 (1919), in his studies of C. lindemuthianum, states that appressoria are 

 formed whenever the germ tube comes into contact with a hard foreign 

 substance which acts as a stimulus for their formation. He found no germ 

 pore in the appressoria observed, but noted that the germ tube arose 

 from the side in contact with the glass. He observed the appressorium 

 to be sheathed in a mucilaginous coat, which aids it in becoming attached 

 to a foreign substance so firmly that even a jet of water fails to dislodge it. 

 In all the cultures made in fresh nutrient media, the germination was 

 rapid, the germ tubes were as large, or nearly so, as the spores, few or no 

 appressoria were formed, and the subsequent development of the mycelium 

 was luxuriant ; while in water cultures, the germination was slow, the germ 

 tubes were much smaller in diameter, the production of appressoria was 

 abundant, and subsequent development of mycelium was scanty or there 

 was none at all. It is true that appressoria were commonly produced in 

 nutrient media that was becoming somewhat dry and hard, as occurred 

 soon when only a little was poured into a petri dish. When a nutrient 

 medium is poured over a water culture, as suggested by Hasselbring 

 (1906), the appressoria germinate within a few hours and produce a rich 

 mycelial growth. 



Mycelium and spore production in culture 



Under favorable conditions for growth, the germ tube branches to form 

 hyphae, and these in turn, by further growth and branching, develop 

 within forty-eight hours into a mycelial mat often one millimeter in 

 diameter. In three or four days conidia are produced at the ends of 

 the hyphal threads. In several agar cultures in this experiment they 

 were produced abundantly on short threads within twenty-four hours. 

 They are formed by the constriction of the wall near the extremity of 

 the hypha. A spore thus formed is pushed aside and the hypha elongates 

 to about the same point, when constriction again occurs. In this way 

 several spores are formed from a single branch, and can be seen lying 

 side by side or piled in a heap at the end of the branch (Plate III, 5). 

 Atkinson (1895:309) observed conidia being produced directly on the 



