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surface; for example, one had a fork hole and another had connection with dry, rotten spots on the surface. However, in two tubers which were carefully examined there was no connection between the cavity and the surface. In these, the blackened tissue was free from fungus hyphae and bacteria so far as could be determined by microscopic examination."
The nature of this potato trouble was long a mystery; but it is now clear that it was a case of blackheart due to lack of air.
Another noteworthy occurrence of blackheart among potatoes stored in a pit is that recorded by Güssow.1! This happened at Ottawa, Canada, on the Central Experimental Farm. Some potatoes stored in a pit were severely affected with blackheart while others of the same lot stored in a root cellar and a heated barn were unaffected. The temperature of the pit was taken daily by means of a self-recording thermometer located near the center of the pit. The highest temperature recorded was 46.5° F.; the lowest, 32.5° F. When the pit was opened it was found that some of the tubers on top had frozen. Since the highest temperature in the pit was far below that required for blackheart (according to Bartholomew) it was necessary to account for the occurrence of blackheart in some other way than by high temperature. In the root cellar and barn, where the potatoes were not affected, the temperature had not fallen below the freezing point; while in the pit some of the tubers had certainly been subjected to freezing temperature. Observing this and lacking a better theory Güssow was disposed to regard frost injury as the cause of the blackheart.
Notwithstanding it is distinctly stated by Güssow that good ventilation existed in all three places of storage " the writers are confident that the potatoes in the pit lacked air and that the blackheart was due to asphyxiation.
Thru the kindness of Messrs. B. E. Smalley of Interlaken and J. Q. Wells of Shortsville the writers have had an opportunity to examine tubers stored in unventilated pits during the winter of 1914-1915. In both cases the tubers, which were unsprouted at the time of removal from the pit, afterward sprouted normally and were unaffected by blackheart.
u Güssow, H. T. Report of the Division of Botany. Canada Expt. Farms Rpts. 1914:831-849. 1915.
AN EXPERIMENT WITH POTATOES IN UNVENTILATED PITS.
During the winter of 1915-1916 the writers conducted an experiment with potatoes in unventilated pits. Three pits containing ten bushels each were used. On November 15 the potatoes were placed in conical piles and covered first with a layer of oat straw and then a layer of clay loam soil. In the center of each pile there was placed a glass tube one-half inch in diameter. The lower end of this tube was about four inches above the bottom of the pile and its upper end projected about two feet above the top of the pile. In each tube a thermometer attached to a string was lowered to the bottom. The tops of the tubes were closed with rubber stoppers.
On December 1, after the first layer of soil had become frozen, a second layer of straw was applied and over this a second layer of soil. The covering of the three piles was made as nearly uniform as possible and no thicker than necessary to protect the potatoes from freezing. It was planned to apply an additional covering of coarse stable manure in case the weather became very cold, but the winter being a mild one this was not needed.
At the time of the second covering two of the tubes were accidentally broken. Hence, it was possible to obtain the temperature in only one of the pits. At irregular intervals of a few days the thermometer in this pit was drawn up and read. The temperature of the outside air was recorded at the same time. (See Table IV.) During February and March the pits were deeply covered with snow most of the time.
On May 5 one of the pits was opened. The tubers were wet all over. Those at the top had sprouts one-fourth inch long, while in the bottom of the pile sprouting had barely begun. All of the tubers were in good condition - free from blackheart and external blemishes.
Another pit was opened on May 26 and the third on May 27. In both pits the tubers were sprouting vigorously. Tubers on the surface had sprouts 2–4 inches long; those on the interior 1–2 inches long. Occasional sprouts were decayed, but the great majority were in good condition. The tubers themselves were sound and normal. Very few had external blemishes and none showed the least sign of blackheart or cavity formation internally.
The excellent condition of the tubers in the last two pits was surprising. Having previously opened Tanks E and F of the seventh
tank experiment and found a large part of their contents ruined by blackheart and decay (page 353) the writers expected to find the potatoes in the pits in as bad or worse condition. This was expected because the potatoes in the pits had been confined almost as long as those in the tanks and the temperature of the pits had been slightly higher than that of the tanks most of the time. That the temperature of the pits was actually higher than that of the tanks, as indicated by the temperature record (Table IV), is proven by the greater length of the sprouts in the pits. They were 2-4 inches long, while those in the tanks were only one-fourth inch long. The potatoes were of the same variety, grown in the same lot and similarly treated up to the time of beginning the experiments except that the tubers used in the tanks were washed, while those used in the pits were not washed.
Thus, it appears that the tubers in these small, unventilated pits were better aerated than tubers at a depth of three to six feet in tanks open at the top. It seems impossible, but it must be true. Had the pits contained larger quantities of tubers or been more deeply covered the results might have been different.
IS THE INJURY DUE TO THE ABSENCE OF OXYGEN OR
TO AN EXCESS OF CARBON DIOXID? Respiring potato tubers consume oxygen and give off carbon dioxid. Carbon dioxid being slightly heavier than air has a tendency to settle. Hence, it is probable that a considerable quantity of carbon dioxid accumulated in the lower portions of the galvanizediron tanks used in the tank experiments. Certainly, in sealed containers, the carbon dioxid produced remains in contact with the tubers, because it cannot escape. Now, the question arises: May it not be the accumulation of carbon dioxid rather than the absence of oxygen which causes the discoloration, blackheart and death of tubers suffering from insufficient aeration?
An attempt was made to obtain an answer to this question from experiments with tubers in sealed containers so arranged that the carbon dioxid evolved was absorbed as fast as produced. Two such experiments were made – one in February, 1915, the other in March, 1916.
In the 1915 experiment two glass jars were used. First, 250 cc. of a 40 per ct. solution of sodium hydroxid was placed in the bottom of one jar and an equal quantity of distilled water in the other. Next, a wire-cloth support to keep the potatoes from touching the liquid was put into each jar, and on top of this twenty-five tubers weighing fifty-six ounces. Finally, the jars were sealed with melted paraffin. They were held in this condition fourteen days at a temperature of 14-21° C.
A heavy, white precipitate (afterward tested with HCl and proven to be sodium carbonate) formed in the bottom and also on the surface of the sodium hydroxid solution. The jar was shaken once a day to keep the surface layer of this precipitate broken up.
When the jars were opened at the end of fourteen days the tubers in the one containing sodium hydroxid solution were nearly free from moisture and a few had a slightly wilted appearance, while those in the other jar were all moist over their entire surface. No sprouts had started in either jar. Upon exposure to the air both lots of tubers soon became discolored in the usual manner, those from the sodium hydroxid jar being distinctly more severely affected than those from the other jar. Eight days after removal from the jars the tubers were cut and examined for blackheart. Those from the sodium hydroxid jar showed 100 per ct. affected with blackheart; those from the jar containing distilled water, 64 per ct.
In the second experiment the containers used were a galvanizediron cylinder having a capacity of about seven quarts and a glass jar holding about 3.5 quarts. Both were provided with tightfitting covers. Two hundred and fifty cc. of a 33 per ct. solution of sodium hydroxid were put into the cylinder, and 250 cc. of distilled water into the glass jar. Twenty-nine tubers weighing 100 ounces were put into the cylinder over the sodium hydroxid, and sixteen tubers weighing 53.5 ounces into the glass jar over the distilled water. Wire-cloth supports were used to keep the potatoes up out of the liquids, as in the preceding experiment. Both the cylinder and the jar were made air-tight with paraffin and then exposed to a temperature of 15-21° C. for thirteen days.
All sixteen of the tubers in the glass jar were more or less moist on the surface. Six were moist over about one-third of their surface, while the remaining ten had moist areas of less extent. After a few hours' exposure to the air all showed the usual discolored areas of various sizes, in some cases as much as one-third of the surface being involved. All were affected with blackheart.
One tuber in the cylinder containing sodium hydroxid solution had a moist area covering one-third of its surface, but the other twenty-eight were dry. Most of the tubers were considerably shriveled and pitted at the bud end when first removed from the cylinder. Upon exposure to the air the entire bud end turned brown, giving the appearance on the surface) of an attack of lateblight rot. All were affected with blackheart quite as severely as the tubers over distilled water. In this experiment no precipitate formed in the sodium hydroxid solution.
It is believed that in both experiments the quantity of sodium hydroxid solution was abundantly ample to absorb all of the carbon dioxid given off. In the second experiment it must have been more than four times as large as required. Yet the severity of the discoloration and blackheart was not lessened. This seems to prove that it is not carbon dioxid which causes the injury.
The cause of the peculiar shriveling and pitting of the tubers over sodium hydroxid solution in the second experiment was not determined.
BLACKHEART ALSO A SHIPPING PROBLEM.
Bartholomew has pointed out that blackheart sometimes results from the overheating of potatoes during shipment in stove-heated cars. Recently, an instance of this kind came to the attention of the writers.
In February, 1917, the Station received a complaint concerning blackheart among a lot of seed potatoes shipped from Clinton county, N. Y., to Peconic, Long Island. A few sample tubers which accompanied the complaint appeared nearly or quite normal externally, but had large areas of blackheart within. It was stated that about 25 per ct. of the tubers in a shipment of eighty sacks (220 bushels) were similarly affected. In some sacks as much as 90 per ct. of the tubers were affected while other sacks were entirely free from the trouble.
The sender was informed that the symptoms indicated that the tubers had been overheated. Upon being requested to furnish information concerning the treatment of the potatoes during shipment he replied that the sacks of potatoes were packed in saw-mill refuse in a car provided with air chambers on the sides and bottom. He stated that inquiry at the shipping point had elicited the information that after the car was loaded the temperature suddenly dropped