294 Diseases of Greenhouse Crops 



water drops produce a chill which causes the content 

 of the underlying cells to plasmolyze. This is fol- 

 lowed by the precipitation of tannin and the disin- 

 tegration of the cells. The method of control would 

 consist in the careful watering of the plants during 

 cool weather. 



Orchid Deterioration 

 Cause, cultural. 



Florists are aware of the fact that imported or- 

 chids often run out and deteriorate after a year or 

 two of culture under glass. Attention has been 

 called to a similar trouble by Truffant and Hebert.* 

 They maintain that deterioration is due to an in- 

 crease in the percentage of mineral matter and a de- 

 crease in the percentage of nitrogen in the deterio- 

 rated plants. The trouble, it is believed, is due 

 largely to improper nutrition under cultivation. 



Leaf Spot of Orchids 

 Cause unknown. 



This disease is often found on hybrid Calanthes. 

 It is manifested as large and small dead patches 

 on all the parts of the plant. The leaves especially 

 become unsightly, and as a result the blossoms are 

 small and stunted. This disease was first described 

 by Bidgood t on greenhouse hybrid Calanthes. The 



♦Truffant, G., and Herbert, A., Jour. Soc. Nat. Hort. France, 19: 

 85-98, 1897. 



t Bidgood, J., Jour. Roy. Hort. Soc. 29: 124-137, 1904. 



