14 BITTER PIT INVESTIGATION. 



CAUSE OF THE DISEASE. 



There are various fruit spots of the apple undoubtedly due to fungi, but the one we are now 

 considering is non-parasitic and external in its origin. It is therefore quite distinct from the fruit 

 spot due to Cylindrosporium pomi (Brooks) on the one hand, and from an internal physiological disease 

 such as Bitter Pit on the other. 



Norton (9) has shown that typical spots may be produced by the action of gases, and he has 

 suggested the possibility of ammonia from the cooling apparatus in cold storage being a common 

 cause of "Jonathan Spot." But, as he points out, the spot may appear on the fruit while still on the 

 tree, and therefore there must be other causes. 



It has sometimes been attributed to injury from an arsenical spray, but that theory was disproved 

 by extensive spraying experiments carried out by the United States Department of Agriculture. 



One of the most probable causes is that of sudden chilling of the fruit, and this may account for 

 the appearance of the spots, both while the fruit is on the tree and in store. When the fruit is fully 

 ripe and the weather moist, the rapid drying of the fruit by a cold wind would tend to produce "spot- 

 ting." The same result would happen if the moisture on the tough skin of the Jonathan were to 

 evaporate rapidly. If the apples are picked when wet, and placed in that condition in cold storage 

 without allowing the moisture to evaporate, then there is a danger of the spot appearing. 



PREVENTIVE MEASURES. 



This is only a side issue to the Bitter Pit investigation, and no direct experiments have been carried 

 out in connection with it. 



In the United States of America, where this disease is very prevalent, there are no definite 

 measures recommended for its prevention, and in the absence of unanimity as to the cause this is not 

 to be wondered at. 



From the conditions under which it occurs here the following suggestions may be offered : To 

 pick the fruit, as far as possible, in dry weather ; to see that it is not too ripe at time of picking ; and 

 any moisture on the fruit should be allowed to evaporate before placing in cool store. 



STIGMONOSE. 



"Jonathan Spot" is clearly distinguished from Bitter Pit, because there is no browning of the 

 tissue beneath the skin, and it is purely a skin disease. In Stigmonose, on the other hand, due to the 

 punctures of insects, not only is there a "spotting" of the fruit, but a browning of the tissue beneath 

 the skin, and to that extent it resembles Bitter Pit. 



About the beginning of the twentieth century the theory of insect punctures and the injection 

 of a poison as a cause of disease in plants was established on a scientific basis. In 1900 Woods (10) 

 found a "spotting"' of the leaves of carnations to be due to this cause, and on making a section of the 

 leaf the sucking apparatus of the insect was found in the tissues. The spots were mostly produced 

 by Aphides and Thrips, and the name of "Stigmonose" was given to the disease. In 1901, by a 

 curious coincidence, both Professor Mangin, in France, and Dr. Cobb, in Australia, attributed the 

 disease now known as "Bitter Pit" in apples to the punctures of insects. Dr. Cobb at first attributed 

 the disease to the Harlequin Bug, but afterwards discarded it, while in France the insect theory of the 

 disease is still maintained. Insects may puncture the fruit and produce "spotting," but this is so 

 distinct from the genuine Bitter Pit that there need be no confusion between the two (Figs. 31, 33). 



Further, it has been clearly shown that Bitter Pit may be developed under conditions in which 

 insects are excluded, apart altogether from the different symptoms. 



In my first Report an apple tree is shown in which 58 clusters of fruit are enclosed in white calico 

 bags (Report 1., Fig. 111). The fruit was enclosed as soon as it had set, and thus the access of insects 

 as well as the possibility of an arsenical spray reaching it was guarded against. The fruit enclosed in 



