77 



the .sjriiwiiis season of tlii' host tlie (-inkers Inereaso raiii<ll.v and are fully 

 grown by the last of Jnne. or a little later. When niatnre the fungus has 

 involved the overlying epidermis, so tliat the outer portion of the canker is 

 aliciut the same size as the area of infested cambium beneath. 



At tirst the cankers are circular, but later they become oblong in outline 

 and nearly black in inlnui'. When the cankers are mature in size the bark 

 becomes dr.v and brittle and the dead tissues separate from the surrounding 

 living ones, leaving a marked fissure. Be.voiid this tissnre the fungus never 

 spreads. 



The mature cankers measure ime-funrth of an inch tn sj.v inches or more 

 in length by one-fourth to five or more inches in width. Very often they 

 a|i]iear to be of much larger dimensions, but. as a rule, the larger ones are the 

 result of two or more cankers merging together. 



After the cankers are full grown the rest of the life of the fungus is 

 spent in maturing the .spores. The first indicatidu nf the formation of spores 

 is a slight roughening of the epidernns at the centre of the canker, caused by 

 the developing pustules. Later, other pustules appear nearer the margin, so 

 that there are. near tlie clo.se of the season, spores in all stages in a single 

 canker. When tlie pustules are mature the over-l,ving epidermis has 

 rnjitiired. exposing a creamy white mass whicli later becomes l:)lack. This 

 mass is composed of hundreds of spores and a .substance soluble in water. 

 As the older pustules open first, spores are discharged from a single canker 

 for a considerable period of time. The bark remains on the tree for a time 

 and then droi)S out. leaving a .scar. 



Remedies. 



Viittiiii/ out tlie Cinikcr.s. — Removing the cankered liark is .-in expensive 

 anil laborious method. It is po.ssible to keep the disease in check on snuill 

 young trees, when little diseased, b.v keeping all the cankers cut out. When 

 the trees are large and have hundreds of cankers mi them, with new ones 

 appearing from November to February, it is impossible to keep the disease in 

 check by such a method. In some eases the fungus matures sjiores in the 

 s,-i|iwood even after the infested bark has been removed. 



Double strength Bordeau.x proves to be a valuable ]irevcntive wlieii 

 applii'il before the fungus ntt.acks the trees in autuiiin. — Wiisliiiii/toii E-rperi- 

 iiieiitiU t<tution, Bulletin Xa. tili. 



Applh AKn I'i:.\K <'.\ncer (Xeetiiria (litissinia.) 



Old canker-eaten trees which are, commercially, absolutely useless, are 

 fre(piently left quite neglected from .year to .vear. These only serve as 

 nurseries for the spread of the disease for miles around, as the minute spores 

 of this fungus can easily be blown for long distances by the wind. One of the 

 main rensdiis for this aiijiarcnt apathy is that man.v fruit-growers look upon 

 canker as caused through some special physical condition of the soil, and not 

 as the result of attack b.v a iiarasitic fungus. Thus the.v consider that pre- 

 ventive measures are quite beyond their control, and they do not rank this 

 affection as a contagious disease and one that by the employment of certain 

 methods can be kept well in check. 



