256 Diseases of Greenhouse Crops 



wedge shaped, reddish-brown spots extending hr- 

 wards from the cleft of the pinnse. Aflfected plants 

 take on a variegated appearance and are less luxuri- 

 ant, but otherwise seem healthy. According to Clin- 

 ton* the scorching may not necessarily be the effect 

 of burning by the sun's rays. It seems, nevertheless, 

 due to the loss of moisture from drought caused by 

 poor watering or to sudden changes of humidity in 

 the air. The fern Adiantum farleyense is very deli- 

 cate, and its thin leaves are more sensitive to un- 

 favorable conditions. 



Yellows 



Caused by overwatering or too much nitrogen in 

 the soil. 



Symptoms. Diseased plants lose their green color 

 and turn white. Growth ceases and all leaflets even- 

 tually drop off (fig. 54). 



Control. In repotting the plant into new soil it 

 outgrows the disease. 



Damping Off 



Caused by Pythium intermedium De By. 



This disease attacks young fern prothallia. The 

 latter turn soft, limp, and darker in color than 

 the healthy ones. In general structure the organism 

 resembles Pythium de Baryanum. It differs, how- 



• Clinton, G. P., Connecticut Agr. Expt Sta., 31st and 32nd Ann. 

 Kept.: •549-350> iJoS- 



