ANNUAL REPORT, 1937 71 



Commercial garden varieties of snapdragons sold as rust-proof strains showed 

 a high degree of resistance to rust, but such varieties are still in need of further 

 selection for trueness to color and type of plant growth. Of 25 varieties tested, 

 only six showed a high degree of purity in color and type of growth. 



Some 35 commercial varieties of greenhouse snapdragons were tested for rust 

 resistance under glass and, while there was some difference in degree of sus- 

 ceptibility, none were observed to be resistant. There was considerable variation 

 in germination of seeds of commercial varieties which appeared to be due to 

 immaturity of the seed. 



Work with the development of Field Station strains of rust-resistant snap- 

 dragons is progressing. Winter flowering types which show promise have been 

 developed for use under glass. Considerable difficulty has been experienced in 

 getting rust resistance, color of flower, type of spike, and the winter-blooming 

 character combined in one strain. 



Study of the Effect of Plant Nutrients, Soil Reaction, and Light on Gardenias. 



(Harold E. White, Waltham.) On the basis of experimental results, preventive 

 rather than corrective measures appear to be a more practical method of regu- 

 lating iron chlorosis of gardenias. For three years it has been possible to prevent 

 iron chlorosis consistently by keeping the fertility level of the soil low and by 

 using a fertilizer mixture containing nitrogen in the form of organic materials 

 such as tankage, milorganite, cottonseed meal, or in the form of ammonium 

 sulfate. Fertilizer containing as low as 1 percent of nitrogen from sodium nitrate 

 or calcium nitrate was sufficient to cause chlorosis. It is questionable whether an 

 actual deficiency of iron occurs in the soil or whether iron compounds remain 

 inactive in the soil. W^hat would appear to be a more plausible explanation of 

 chlorosis in gardenias is that antagonism between iron and certain nutrient 

 elements — possibly calcium or sodium — takes place within the plant. Sulfur 

 in a quantity as low as one half pound per 100 square feet of bench area was 

 sufficient to prevent chlorosis; however, in quantities above one pound it had a 

 definite retarding effect on the growth of the plants. 



Phosphorus and potassium do not appear to have any influence on chlorosis. 

 Added illumination of 25 to 50 foot-candles of light for 6 hours each day from 

 September 1 to April 1 had no efTect on chlorosis. Low growing temperatures were 

 observed to produce a type of chlorosis which did not respond to iron treatments 

 to the foliage and did not appear to be corrected by applications of ammonium 

 sulfate. 



Analytical data on chlorotic and normal plants show that plants fed with 

 sodium nitrate were lower in iron content than plants fertilized with ammonium 

 sulfate; also, sulfur increased the iron content of plants even though they were 

 fed with sodium nitrate. Soil acidity does not appear to be a specific cause of 

 iron chlorosis, as chlorotic symptoms occur over a wide pH range. 



Propagation Studies with Gardenias. (Harold E. White, Waltham.) Tech- 

 nique and propagation methods do not appear to be concerned appreciably with 

 the successful rooting of gardenia cuttings. 



Propagation Studies with Geraniums. (Harold E. White, Waltham.) Losses 

 of geranium cuttings by florists who propagate plants would appear to be due to 

 tlack stem rot disease. Isolation and inoculation studies indicate that several 

 fungus organisms are concerned in the rot of the cuttings. Treatment of the 

 cuttings with different disinfectants and the sterilization of the propagating media 

 had no effect in reducing the rot disease. Synthetic growth substances did not 

 appreciably stimulate rooting of geranium cuttings. 



Temperature experiments relating to the rooting of geranium cuttings show 



