Apr. 15, 191S A Leaf blight of Kalmia latifolia 209 



stromatic surface of a culture on steamed com meal. With sterile 

 forceps these were freed from the stroma, placed in a tray, and bisected. 

 One-half of each of these pycnidia-like bodies was at once fixed in Car- 

 noy's fluid, and later embedded in paraffin. The corresponding half in 

 each case was placed in a petri dish of corn-meal agar, or of com meal. 

 They were examined daily, and in all the experiments more than two- 

 thirds, and in four experiments all of the bodies transferred produced 

 spores in from 4 to 10 days. Rapid growth of mycelium always oc- 

 curred in the transfers to dishes of steamed corn meal, but only about 

 5 per cent produced spores. In this medium the pycnidial bodies be- 

 come covered with a white, dense mat of hyphae and the surrounding 

 medium is likewise overgrown with a thick stromatic layer. Such is 

 not the case when corn-meal agar is used; only a very delicate fringe- 

 like grov/th around the pycnidial bodies occurs, and their surfaces are 

 not overgrown. This again goes to show that the character of the 

 medium has much to do with the form and the fertility of these stmc- 

 tures. As soon as spores were extruded, the bodies were fixed in Car- 

 noy's fluid, embedded in paraffin, and sectioned to determine from what 

 portion the spores had been produced. It was found that the portions 

 of the sterile bodies showing the nucleated hyphae were the points from 

 which the spores originated (Pi. 17, A). It has been obsen-ed in the 

 cultural studies made that these sterile bodies are produced only when 

 the culture medium is of such character as to stimulate extremely rapid 

 and abundant vegetative growth — that is, the stromatic surface becomes 

 crowded, and possibly the oxygen or moisture requirements are inade- 

 quate. It might also be a question of food, since between the actively 

 growing spore-potential cells lie a mass of dead cells resting upon a hard, 

 dry stroma, frequently raised above the surface of the medium. 



The sterility of these bodies might, too, be due to the production of 

 toxic substances by the rapid mycelial growth. The central portion of 

 the flasks where growth is more rapid is usually where the majority of 

 the sterile bodies occur, the more scattered pycnidia on the margins 

 producing spores in an almost constant ratio. 



It should be noted that the object in sectioning one half of these 

 sterile bodies when placing the other half in the culture medium was to 

 determine absolutely that they were not then producing spores, and 

 also to study the structure of each for comparison with the other half 

 after it had fruited. 



A few experiments were made to determine the effect of limited air 

 supply upon the production of spores by these sterile pycnidia. About 

 100 of these bodies were bisected and arranged in rows on petri dishes 

 of corn-meal agar. One half of each sterile pycnidium was left un- 

 covered in the dish and the other half covered with sterilized slides or 

 cover glasses. After five to seven days all of the bodies left uncovered 

 in the dish were extruding masses of spores (PI. 16, C), while those covered 

 had produced no spores and only about one-third as much mycelium. 



