MYCOLOGICAL SECTION. 227 



Another vulnerable point for the attack of blight is at the growing 

 tips of the branches, or at any point where there are developing bnds. 

 At such places the tissues, including the epidermis, are tender and 

 filled with nutrient sap, while the outer surface of the organ is not 

 yet cuticularized and rendered impervious. As the shoot ceases to 

 elongate and approaches maturity the chances for infection become 

 less and less. The early part of the season is consequently the most 

 dangerous part, and allowing for the incubation period, during which 

 the disease is inconspicuous, its strongest manifestation naturally 

 falls in June and July. As the growth at the extremities is more 

 vigorous or more protracted the possibilities of infection are corre- 

 spondingly increased, and a "growing season" is likely therefore to 

 be a blight season. A connection between immaturity and blight 

 has long been suspected, but explanations of the matter have hereto- 

 fore been erroneous. 



Besides the two vulnerable points already mentioned, there may 

 now and then be another, brought out by cracking or other injury of 

 the bark, and occurring on any part of the tree, but more commonly 

 on the trunk. Through these cracks, however minute, the germs 

 gain access to the interior of the tree, and the disease is started. The 

 after progress is usually slow, on account of the solidity of the tis- 

 sues, and progressing about equally in all directions, forms a patch of 

 dead bark, which becomes dry and hard, often somewhat sunken, and 

 usually separated from the living bark by a well-deiined outline or 

 crack. Such injury is commonly known as sun scald, and has been 

 specially studied by Professor Burrill, to whom we are indebted for 

 our knowledge of its origin. The spots occur most abundantly on 

 the southwest side of the tree, being the side which is most affected 

 "by the heat of the sun. The cracks through which the germs first 



fain access are the result of the drying out and contraction of the 

 ark, and in so far the injury is due to the sun, although in no sense 

 a "scald." Blight upon the trunks and larger limbs is also often 

 contracted from small short spurs with a few leaves, which admit the 

 germs at the time the spring growth is taking place. 



Preventives and remedies. — "Whatever form Pear Blight assumes, 

 it is started by germs gaining access to the tree in one of the three 

 ways described— through the flowers, the growing shoots, or injuries 

 of the bark. No method is known or has yet suggested itself of ren- 

 dering the tree insusceptible to the disease, and a direct prevention 

 must be sought in some means of excluding the germs. There are 

 three ways by which germicides may be applied to trees — by fumiga- 

 tion, by spraying, and by washing. The first method offers a pos- 

 sibility of at least partial success, and appears to be the only means 

 by which one can hope to protect the flowers. 



The trials made so far have been with sulphur mixed with lime, and 

 applied as a wash to the trunks. It is claimed by careful orchardists 

 that the odor of the sulphur can be detected for weeks after treatment, 

 and that it has proved satisfactory in warding off the disease. Whether 

 more thorough and extended experiments will substantiate this con- 

 clusion, or show that the supposed immunity comes from other and 

 accidental causes, there is yet no firm basis for an opinion. 



Spraying offers little more hope of success than fumigation. The 

 inner surface of the flowers are so well protected by the stamens and 

 other organs that the antiseptic used does no service. The growing 

 shoots have their tenderest parts j^artially protected with the terminal 

 cluster of leaves, and a fresh surface is continually forming which it 



