1628 



ENCYCLOPEDIA OF PRACTICAL HORTICULTURE 



sap, so that the conditions which favor 

 the growth and production of the fruit 

 also tends to favor the germ; for we 

 must remember that the germ is itself 

 a plant, depending upon the rich food 

 supplied by the tree for its best growth. 

 The fleshy bark of trees grown under 

 constant sunshine, especially those of the 

 Pacific coast, seem to be richer and 

 thicker than in the Eastern states, and 

 naturally affords an unusually good feed- 

 ing ground for the pear-blight bacillus. 

 This rich, fleshy bark also tends to hold 

 over the germ during the dormant season 

 in a much more serious way than the 

 thinner bark of trees grown under other 

 conditions. Cloudy, rainy weather, there- 

 fore, while favoring infection, sometimes 

 results in a starved condition of the tree, 

 which, of course, is especially unfavor- 

 able to the pear-blight germ. Trees 

 grown so as to produce a minimum 

 growth naturally are short of plant food, 

 and of course do not favor the pear- 

 blight germ, even though it should enter 

 the tissues. Every physiologist knows 

 that in order that a green plant may 

 form starch in its foliage the action of 

 sunlight is required. The more intense 

 the sunlight the more rapidly the forma- 

 tion of starch goes on. In cloudy, dark 

 weather very little starch is made or 

 elaborated in the leaves. Of course, we 

 know that the tree does not make use 

 of its starch as such, but, through the 

 action of a diastatic ferment or enzyme 

 the starch Is changed into sugar, which 

 is translocated to all parts of the tree 

 by osmotic action; that is, through the 

 sap. It is this rich sap, which is mostly 

 sugar, that the pear-blight germ feeds 

 upon. The more sugar, the more intense 

 the destructive action of the germ. The 

 very regular growth of the trees in the 

 Rocky mountain and Pacific coast or- 

 chards tends to keep the pear-blight germ 

 continually at work, unless checked by 

 prompt and thorough eradication. In 

 the Eastern orchards, especially with 

 dwarf pears, which make their growth 

 early in the season, a heavy rain, if ac- 

 companied by a day or two of cool, 



cloudy weather, will cause the trees to 

 form their terminal buds. 



Before leaving the discussion of 

 weather conditions, it may be well to 

 point out more fully the reasons why se- 

 rious outbreaks of blight occur after 

 showers or thunder storms. It has been 

 the common belief that static discharges 

 of atmospheric electricity have a consid- 

 erable influence upon such outbreaks. 

 This, of course, is mere fancy and has 

 no scientific significance whatever. Every- 

 one knows that a seed planted in dry soil 

 cannot germinate unless moisture is ap- 

 plied to it, either artificially or naturally. 

 Now, supposing a thunder storm comes 

 along with a heavy precipitation, or at 

 least sufficient precipitation to moisten 

 the soil about the seed, what happens? 

 The question is so simple that a child in 

 the primary grade would not hesitate in 

 answering it. Of course, the seed starts 

 into growth, the rapidity of its growth 

 depending upon the temperature follow- 

 ing the rainfall. Now, was it the rainfall 

 or the thunder and lightning that caused 

 the seed to germinate? It was the rainfall 

 and the warmth, and nothing else. It 

 has been explained that a germ or bac- 

 terium is also a plant, dependent upon 

 moisture and heat for its growth. In a 

 dry season an enormous number of in- 

 fections may take place, but the very fact 

 that the season is dry and warm accounts 

 for the fact that these infections fail; 

 just the same as in a very dry season a 

 very large percentage of corn, or any 

 other seed put into dry ground, will fail 

 to germinate and we have an occasional 

 plant coming up, just as we find in the 

 case of blight, only a few infections ap- 

 pearing. Everybody knows that after a 

 rain every vegetable starts into rapid 

 growth providing the weather is warm. 

 Now, rapid growth in a pear or apple 

 tree means nothing more nor less than 

 an enormous addition of water, plus food 

 from soil and air to it. Here we have 

 conditions favorable to the growth of the 

 blight germ, which uses the pear or apple 

 as its soil from which it draws its water 

 supply and its necessary food, namely, 

 starch and sugar. Just preceding a heavy 



