Mar. 3, i9»3 
Gray Mold of Castor Bean 
699 
In addition, several castor-bean stalks were found (July 21 and Aug. 
1) with sclerotia still attached producing apothecia in great abundance 
(PI. 6, D). It has been seen that each apothecium is capable of dis¬ 
charging spores in a distinctly visible cloud. It is clear, therefore, that, 
even were the conidial stage not capable of living over the winter, the 
apothecial stage thus produced would be capable of starting an abundance 
of primary infections. 
CONCLUSIONS FROM EXPERIMENTS 
These experiments and observations bring out the following points of 
interest in connection with the development of apothecia of this organism 
under controlled conditions: 
(1) Moisture. Reasonably moist conditions must prevail, both in the 
substratum upon which the sclerotia are resting and in the air above. 
(2) Temperature. While a wide range of temperature will permit of 
their development, most rapid growth occurs under fairly warm condi¬ 
tions, averaging about 25 0 C., the optimum for the vegetative growth of 
the organism. 
(3) Aeration. Provision must be made for access of air to the 
sclerotia; too small an air space above them, as for instance that which 
would be found in a covered Petri dish is not as favorable as a greater 
amount, other things being equal. 
(4) Light appears to be necessary, both as an initial stimulus and for 
continued normal development; those developed with insufficient light 
are long, slender, and irregular and do not open up normally. 
(5) Subjecting sclerotia to freezing, drying, or an extended dormant 
period previous to placing them under favorable conditions does not 
favor apothecial development. 
(6) The fungus is purely homothallic. Sclerotia from single spore 
cultures develop apothecia as readily as do those from mixed strains. 
MORPHOLOGY AND PHYSIOLOGY OF THE PERFECT STAGE 
It is hard to distinguish the apothecium macroscopically from that of 
any other Sclerotinia. It is smaller, on the whole, than those of the 
well-known forms Sclerotinia libertiana and S. cinerea , the largest seen 
having a disk only 7 mm. in diameter; the stalk normally is only 1 or 2 
cm. long. The disk or cup is not so often funnel-shaped as it is with the 
other two forms, but it is more frequently opened completely or even 
recurved, as shown in Plate 11, C, and in Plate XL of the writer's earlier 
paper (jo). The color is that of most Sclerotinias and varies somewhat 
from cinnamon brown to chestnut brown, the stalk sometimes being 
lighter, sometimes darker. From one to several may be borne upon a 
single sclerotium. 
Any unfavorable condition that may arise while apothecia are forming 
may cause strange abnormalities in their structure. They often fail 
entirely to open out, the tip being tubular for a short distance back. 
Such forms have no normal asci, but rather hyphal tips resembling the 
ordinary paraphyses. Another abnormality that has been observed 
after a temporary check in the growth of an apothecium has been a 
division near the tip into several distinct cups. Sometimes these have 
failed to mature, and again they have developed several normal mature 
ascus-producing disks. Plate 11, D, shows an apothecial stalk with 
five distinct disks. 
