GROWTH IN CULTURES. 23 



The germ tubes grow in length with great rapidity, reaching a 

 length three or four times that of the spore (PL V, fig. 2) in three- 

 fourths of an hour. In a water medium the first hyphse grow to con- 

 siderable length before branching. In bouillon or agar they branch 

 when two to three times as long as the spore. Septa form very early 

 in the development of the mycelium (PL Y, fig. 2). 



Fusions between neighboring hyphse are common both in the apple 

 fruit and in cultures. The young hyphse are colorless and are filled 

 with a granular protoplasm. When growing in the tissues of the 

 apple, the young hyphse soon turn darker and ultimately become 

 brown. When an abundant food supply is at hand the mycelium 

 grows to large dimensions, and it may be several days before any 

 fruiting bodies are formed. These are usually conidia formed by a 

 process of abstriction at the end of short lateral hyphae (PL V, fig. 7). 



These conidia develop with great rapidity (Clinton, 1902), so rapidly 

 that in twelve hours an agar plate will appear as if covered with a 

 powdery mass. When growing under unfavorable conditions, so that 

 the mycelium is starved, some of the hyphal tips will swell consider- 

 ably, and a wall will cut off the swollen end (PL V, fig. 2). The walls 

 of this swelling turn dark red-brown and thicken somewhat, forming 

 what appears to be a spore (PL V, fig. 2). A bright translucent spot 

 is usually present near the center. These brown bodies have various 

 shapes and appear to be formed by most species of the genus Glceo- 

 sporium. Miss Stoneman (1898) figures them for G. fructigenum and 

 G. naviculisporium. Miss Southworth (1891) and Clinton (1902) 

 obtained them in cultures of Gloeosporium fructigenum. Gloeosporium 

 cactorum forms very fantastic bodies which bud and develop short 

 tubes (PL V, fig. 4). Halsted (1892) published an extended account 

 dealing with some of these secondary spores. Many attempts were 

 made to cause the bodies formed by Glososporium fructigenum to ger- 

 minate, but so far without success. They probably represent a form 

 of chlainydospore, which may have to undergo a resting period before 

 developing. 



The conidia formed freely from rapidly growing mycelium on agar 

 resemble those from the pustules on apples in all respects. They ger- 

 minate in a similar manner, and the mycelium which they give rise to 

 may produce similar conidia, pustules, or perithecia, as the case may 

 be, depending upon the age of the fungus, the food supply, etc. The 

 fungus can be made to grow continuously, producing crops of conidia 

 without the production of the other stages. 



When kept growing on apple agar several crops of conidia usually 

 form, as described above, and when the food supply has been partially 

 exhausted the production of conidia gradually stops. The first lot 

 of conidia have germinated by this time and have produced mycelia, 

 so that a petri dish with a pure culture of the bitter-rot fungus 



