590 



STATE BOARD OF AGRICULTURE. 



LIGHT RELATIONS. 



Physiological investigations in this field have indicated that, with manj^ 

 species of higher fungi, light is of little importance either as a stimulant or 

 as a repressant of vegetative gro^v^th. With many of these same organisms, 

 however, light is an important and often an essential factor in spore produc- 

 tion. Levin*, working with a number of species of Sphaeropsidales found 

 that while mycelial gi'owth was just as abundant, fruiting was considerably 

 lessened and, in several species, completely suppressed by absence of light. 

 Species of Coniothyrium, Phyllosticta and Cytospora showed considerable 

 pycnidium production in the dark but at that suffered a faUing off of more 

 than 55 per cent when light was excluded. Species of Ascochyta, Phoma, 

 Sphaeropsis, and Fusicoccum produced no pycnidia in the dark. Coonsf 

 has found that, in the case of Plenodomus fuscoinaculans, darkness has little 

 or no effect on vegetative growth, but is prohibitive to pycnidium production. 



With these results in mind, experiments were planned to determine the 

 effect of light and darkness in vegetative growth and pycnidium production 

 in the case of Phoma apiicola. To provide for darkness and at the same time 

 allow for the circulation of air, a method modeled after that of Coons was 

 used. To exclude light, two battery jars were wrapped in heavy black paper. 

 The larger was placed bottom end up over the smaller one and allowed to 

 rest on a block of wood, thus providing for a passage of air at the base and 

 over the top of the jar within. A similar arrangement was prepared, using 

 heavy wrapping paper, for obtaining diffused light. Two jars without any 

 covering were used in the series exposed to light. Filter paper cones were 

 placed in preparation dishes (5 cm. diam.) containing 5cc. of corn meal 

 broth as the nutrient medium. Inoculations were made directly from my- 

 celium. Eight dishes were placed in each jar. Results are tabulated below. 



TABLE 6. — EFFECT OF LIGHT ON GROWTH AND PYCNIDIUM TRODUCTION. 



Pycnidia were produced in greater numbers in light than under any other 

 conditions. It is conclusively demonstrated, however, that light is not an 

 essential factor in the fruiting of this* organism. Light seems to stimulate 

 fruit body production, probably due to the lessening of vegetative growth 

 or to some other indirect action. 



Greatest mycelial development was obtained in diffused light, here also 

 the hyphae were more upright producing a looser and more fluffy mass. In 

 darkness there was apparently as much growth as in strong diffused light. 



* Levin, Ezra. Light and pycnidia formation in the Sphaeropsidales. Report Mich. Acad. Sci. 

 17:134-135. 1915. 



t Coons, G. H. Factors involved in the growth and pycnidium formation of Planodomus fuscomacu- 

 lans, Jour. Agr. Res. 5:713-769. 1916. 



