658 STATE BOARD OF AGRICULTURE. 



masses are similar to those produced in culture. They arise in a spiral 

 form when the 0]>ening is small. When the opening is large, they re- 

 semble those in culture. The leaves do not suffer severely from the pri- 

 mary Infection. When two or three spots are present on a leaflet, it be- 

 gins to droop and the entire leaflet turns yellow. When the spores from 

 these spots have been washed to all parts of the leaf by the dew or rain, 

 infection may again take place and the spots appear just as the leaf 

 shrivels up and dries. If the spores are present in abundance the leaf 

 will die after the first infection, if a large number of spots are formed. 

 This condition is usually present when the tomatoes are allowed to 

 run over the ground. The first condition is more typical of staked to- 

 matoes. The reduction of the photosynthetic area of the plant impover- 

 ishes it and reduces the quantity of fruit produced. The fungus attacks 

 old and new leaves alike, but due to the incubation period of five days, 

 a vine that was almost completely defoliated will have a small tuft of 

 terminal leaves. 



Mortid Physiology : 



The causal organism in its attack on the leaves eventually produces 

 defoliation and the effect of this is evident, not only in the size of the 

 crop, but upon the character of the fruit produced. There is, however, 

 a period when the leaves are spotted but not otherwise affected, and 

 then follows a period in which the spots, while not enlarging, evidently 

 influence the plant, causing a yellowing of the adjacent tissue. 



Work by Galloway (1896) with a rust of pine seemed to indicate that 

 the cause of the vast disturbance of the pine leaves followed by leaf cast 

 was due to the excessive water loss which took place from the rifted 

 epidermis. This conclusion is warranted from his readings. Moreover, 

 the whole biology of the evergreen needle seems to indicate that it may 

 be especially susceptible to a transpiration shock such as must result 

 from a strongly perforated epidermis; but in the tomato disease the 

 epidermis remains intact and the yellowing proceeds very slowly and 

 the leaves do not manifest the characteristics of transpiration shock. 

 Moreover, the recent work by Reed and his associates, Cooley (1913) 

 and Crabill (1915), on Gymnosporangium raises important questions. 

 These investigators did not find an acceleration of transpiration from 

 diseased tissue. 



The conclusions of Reed could not be used directly for the fungus un- 

 der discussion due to the strikingly different habit on the host. Rusts 

 are known to conserve the tissue of the host, at least until after fruit- 

 ing, while with this fungus the host cells attacked were killed in a very 

 few days and previous to fruiting body formation. 



An experiment was conceived which would aim to determine the in- 

 fluence of the disease upon transpiration. Due to the ease with which 

 the tomato plant is infected by this fungus, and also, because of the 

 general structure of the tomato plant, the experiment was possible on a 

 larger scale than has ever been used in similar investigations. Twenty- 

 two tomato plants were grown under identical conditions in the Botan- 

 ical greenhouse from seed of Earliana variety. The soil of the pots was 

 sifted twice before being placed in these receptacles and was saturated 

 but not water-logged. The pots were prepared as follows : 



A number of stiff one-pound cheese cartons (upper diameter 10 cm., 



