THE CANADIAN HORTIODLTDKIST. 



253 



The blighted branches were removed 

 with pruning shears on July 1, by a 

 clay laborer who was none too keen 

 eyed. Ten days afterward the orchard 

 seemed far more blighted than at first, 

 and in many instances it had struck at 

 the bodies of the lai'ger limbs, and in 

 one instance at the trunk below the 

 limbs. 



There was now a marked difference 

 in the amount of blight showing on the 

 several varieties. The Bartlett led 

 them all, some of the laro;er trees being 

 SO much atiected that wljen the diseased 

 branches were removed there was bat 

 little of the top left. 



At first this was puzzling. A care- 

 ful study of the case, however, furnish- 

 ed a solution. Although all had pro- 

 bably taken the blight about equally, 

 yet it had spread thi'ough the tissues 

 at very difierent rates in the difier- 

 ent varieties. The Bartlett showed 

 itself the most susceptible. The ap- 

 parently rapid blighting of large limbs 

 was I'eadily traced to the incur- 

 sions of the disease through the shoi't 

 spurs near their bases. In the less 

 susceptible varieties the disease had 

 not travelled the whole length of the 

 spur at the time of the first pruning, 

 and was therefore all removed. In the 

 most susceptible kinds it had gone 

 the length of the spur and already 

 entei'ed the large limb when the spur 

 was cut away. Here it did not take 

 long to girdle the limb, prevent the 

 passage of sap, and thus practically kill 

 it. In the single instance where blight 

 occurred on the trunk of a tree below 

 the branches, it was perfectly evident 

 that it had entered through a vigorous 

 young shoot that had started out at that 

 point this spring. The failure to cut it 

 away before the blight reached the 

 trunk cost us the entire tree. 



In addition to the out-of-door observa- 

 tions, a very extended course of experi- 

 ments in the house have been carried 



on. It is only necessary to refer to 

 these in the present connection in order 

 to mention the artificial cultivation of 

 the germs of the blight. These have 

 been grown in sterilized infusions of 

 corn meal, hay, barn-yard manure, 

 green fruits, starch, etc. The import- 

 ant point is that they will live and 

 thrive outside the tree in dead organic 

 substances. 



These are the facts. They explain 

 the phenomena of pear blight in this 

 way. The disease is due to living 

 germs. These germs can live and 

 multiply indefinitely in any damp spot 

 where there is decomposing vegetable 

 matter. Fi-om such places they are 

 raised into the air when dry, or carried 

 up by moisture. From the air they 

 lodge upon the trees, and when the 

 conditions are favorable pass into the 

 tissues and cause the blight. The con- 

 ditions referred to are in general (1) 

 very tender tissues, such as are found 

 within the flowers and at the ends of 

 expanding shoots in spring, and (2) a 

 moist atmosphere. No varieties are 

 entirely blight proof, but the disease 

 spreads so slowly in some that they 

 receive little injury, especially when 

 not making too rapid growth. The 

 reason why the blight, when seen in 

 July and later, does not pass directly 

 from one limb to another, or from one 

 tree to another, is because in the ^rst 

 place the germs cannot escape, being 

 confined by the bark, or else escape in 

 a viscid exudation which holds them 

 firmly together, and in the second place 

 there are very few places on the tree at 

 this time of the year where the surface 

 tissues are sufficiently tender for them 

 to find an entrance. 



Does not all this suggest some 

 thoughts regarding pi'eventives and 

 remedies 1 Do not force the tree into 

 too rapid growth by heavy fertilizing or 

 otherwise. Place no confidence in 

 sulphvir, lime, or washes and applica- 



