iMlCiilGAN ACADEMY OF SCIENCE. . 117 



AN UNDKSCRIBED BARK CANKER OF APPLE AM) THE 



ASSOCIATED ORGANISM. 



BY G. II. COONS. 



In March, 1011, sjjeciniens of badly cankered ajjple limits were 

 iiient to the Botanical laboratory of the Michi<>an A^ricnltnral Col- 

 lege from an orchard near Boyne City, Charlevoix County, ^Michi- 

 gan. Examination of the specimens and field studies during the 

 same month indicated that the canker was different from the de- 

 scribed cankers of api)le. Accordingly abundant collections were 

 made and from this material an organism was isolated. Pure cul- 

 tures from a single spore were used successfully in inoculation ex- 

 periments in 1011 and again in succeeding years. The rules of 

 proof of parasitism have been fully complied with. The organism 

 has been used in i)hysiological studies, especial attention being 

 given to the factors which affect growth and reproduction. The 

 work dealing with pathogenesis as well as the physiological rela- 

 tions of this organism are reserved for future pultlication. It is 

 the purpose of this preliminary paper to describe briefly the canker 

 as found upon the apple and the morphology of the causal fungus. 



THE C-\NKER. 



The typical limb canker (PI. VI) associated with this organism 

 is caused by the killing of the cortex in long strips which extend 

 along or Avind about the affected limbs. The killed tissue shrivels 

 and becomes separated from the healthy bark. The strong fibres 

 in the shrivelled portion prevent the flaking off of the dead ])ortions 

 for a year or two but eventually the wood becomes bare. The dis- 

 ease is progressive and year after year the canker encroaches uj)on 

 the healthy, younger tissue. This encroachment is, for the most 

 part, along the limb rather than around it. Accordingly we may 

 find a large limb with as much as one-fourth of its circumference 

 bare. This bare condition extends along the lind) toward the tip 

 and there we find twigs, one, two, or three years old with canker 

 in its first stages. In the early stages of the canker the diseased 

 bark is still in place, but it is separated from the healthy portions 

 by a definite cleft. The bark at the edges of the diseased strip 

 cracks into definite square or rectangular areas of varying sizes, 

 averaging about an eighth to a quarter of an inch across. The 



