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BLACK ROT, LEAF SPOT AND CANKER OF
POMACEOUS FRUITS

A THESIS

PRESENTED TO THE FACULTY OF THE GRADUATE SCHOOL
OF CORNELL UNIVERSITY FOR THE DEGREE OF
DOCTOR OF PHILOSOPHY

BY
LEXEMUEL RAY HESLER

‘Published as Cornell University Agricultural Experiment Station Bulletin 379
August 1916

BLACK ROT, LEAF SPOT AND CANKER OF
POMACEOUS FRUITS

A THESIS

PRESENTED TO THE FACULTY OF THE GRADUATE SCHOOL

OF CORNELL UNIVERSITY FOR THE DEGREE OF

DOCTOR OF PHILOSOPHY

BY
LEXEMUEL RAY HESLER

Published as Cornell University Agricultural Experiment Station Bulletin 379
August 1916

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‘In Exchange,

CONTENTS

PAGE
Sih COMA Cee ict ac ome ea aoa ROI SS Darn manic to Hncrerotomholore 53
- PIES GomGhatte ee oos ates cae Re oe he cites Coin DEE A core er Cl tick: Gaon 53
Varietal susceptibility.............. Soe ak ae Bet er Cet pioics Gelcis Tobe 53
(OF ligontn oul ol tole sO ALAR cn eine Was et otal ae a SA En Oba cnc com AiemS 53
Omtoliaceytoveatspob eps Pere Coors gatteie cs othe: fac iyo e aves ayetce 53
@felinn bsitovGan enone pra rere eo ttt staan: Oleic Pt Woeeerncta 53
“Tike: GUS@AREn bSoo POH BO GOONS Baa an he oO yap Ae CEC Cb OOR TO eEG. ce ADEs On aoe 54.
INGE a ae Gis OB ORAM E RICO eb eae 5.5 tee oath destaganl ss: an edcrsis.Mtaeaay sts sienecmra ates 54
TEKISIO MTs este Saidocton dog op Mee A AOIIrs 6 Oconto DOR eck Gh ern Eres a Etro mean 0G 54
iihtesin| a Gkearo ty Ola ene attire. 2 peteucres ceresmroke teactcanue cecten rch cnate eke Seer Ot eveeseis 54
Mbelechicmo ty eink te were eh atyetcts orien elo cua heran oebN nt rnereerers 55
Mhercamken torn: ches hpeleaa wa sctaeyeie eines soho arian See ope eats 55
Geapmaphicalhocetnren Cea wiia rel iiiens 2 peepee: els fo pete ais ecsashersiel ots 56
PeonomicumportanGes< 2. soc-e-b ee <i eles anes aS ieee aR PL Acts)
(General(considerations’. ms ast dese sce seme astern: = aoe aes 58
Waite Of IOSSESs ene neie so eta ae he eee ek het Seer weer Srey 58
Tiny tiryatOueittiire i vayote eis eras seca ale Ces ar, Be a 58
Inyjuny totoliaze: 2 202.2225. Mahe aalsaen a aicate SR Res Vas 59
Ibstibieyritoy leona OSs cits AB, ERP aie icvtcbice Bi Daye mie Seeon tee DAS 59
SME LOMISt yer athens oleic custetcr pices tates etanes Patna et tates ciokatene 60
Ontbhevintttite virccm.- raneos deo cis eras sr eee ALOU or See cals 60
Onithewleavessyters nics imme eeepc UOTE SoA nie Ben atentene 61
@nirthewimabs sae -tg vee eas GEE Ee tec Dare RS ea eee 62
Other organs affected............. dot Weve RIA ee Cerwin at ath oni Tots Ga ae 63
IB HOGA e Behe don Dene ane Oe Bee TOE En oe aaa ee ete oe Spee oieharenets 64
Mronphologyen .c)cnr cist) seta: Shaoee RET cede ob HELA AS dos atv 64
Renttheei ares ae ga eae oe ea ee bis sdaje wee bee a ee euch : 64
Pycenidian psi sere sree : Re yee rie eae RE tain eee 66
Pyenidialliformaticar 2 .- Pee Cones ee ee cS 68
IP¥CNOSPORES 4s 42 ty seeps es Se er erin ee sen arta ane 71
iy celitiminns tec hss LSet ie Bitte ier him ve bh doayiecteteraraie mene 74
SGlETOliale ry koe ee UR cgs ests ; Le ieiee na er Ree 75
Chilamydospores: .is.2255.2---.-- : : SD ets 22 07 hs)
Microconidia: \) 22-2 20... 6 Ee can nee Oe hs wee 76
sVeastiforms, ssa. = a iota: Rien erst re BEh Reon oan 76
inv stolopyeunestie sce: shale: ¥ Mey pete Tylak aoc eee 77
Methods of isolation. ... See a Et oe Me rao paee “Hl
@ultimall:charactersi=—igeseral 1.8 oi. So eh teens sia ais ati sepeethe Chere = itl
Gulturallcharacters)—— Special f2 assis waetne oil cette tteret 77

Protoplasmic streaming............... ASO ITS 6c tes aE i
Tea lavoseeinblort in ten Oocee eMOR OS ee Me Wes Setar Bae Somat Oe 78
BIACKETOGOmApDIese, pute ato eaten ne ctte cima, e at eet een seers, ana Sec rete 78
eatispotokapplews cm. a. -fabeeisig <tr> cst ese oe aan ee 79
Canker Of apple vr isyecct tes. ksandel teens oon sis are ae Benn nee 87
Cross-inoculations and host relationships.....................-.- 95
INamesrandiSyimoniymiyaeeie go craer: Aenea es sieyen vc ait © chasse Seictaye ake levee © 99
Nei fes history SbUdieSs. Spite meahye lie, oysetegepe eis atthe Stam, os Ben BiG aca igre 101
SCHECE TO Mu MesING CLE a ta yarn ate cnt ghithe © oho elarsh me ginie)a\s sweats IOI
Miethodtospore discharges et. a. kak a incit stint nel wears scl edls 103
PIES OM SHOLECUSChice Coes mremcsiern set a tyate Seutyarnee rare Ole sb iat dlie scvaitrerale 104.
ING Ents) Of CISSeMinaOM Mar sla wate; Sivlsis cas 2 dey ila shia © ye oly Stee wes 105
TREC GIO ME COULT ES ee ewan gate eee Pek oe Patcicj Mansy od hel shiec hehehe auepale ls eue- 4 105
Py CHOS POLE! BEMITIALLOMy wel MME else dle clepe ep cle) Metzivne,s o. a) aie ayete, 01s) ofe 107
PASCOSPOLEP CLiMIna OMe ne ete efey tala sya stesvties <tsia ls) njetovaoi celts «. ova; ccate 108
acu Dat OM ETON ne. emmy Em eee ate share conetvatehats laleVsh cyefaleve 0:0) i eleleloxe 108

52 CoNnTENTS

PAGE
Pathological histology. . 2.2. siete ee ee Co eee 109
ty at eet Pe ena a Rin. it ain boa sind oui A ihc ca ko am aan otese 109
LCE WC ete inc: ORME Oe enn cer. cbiceccie doa tina ALACRA 110
Barks. ses Sanat ayetage Syne eee ee ee ene ere III
Control 5.18 Shot oer kee oe tare Ree eee eee neon: 116
Biack ot. sco ot chee ere eee ees remaster S oto Sf Rootes ae oe 116
ixclusion (byelegislationtts setems weeks serait caer ieee ae eae 116
SPLAT Gai c-2 pra ae Marg sierra se cistnste cS acres. oie coin eee oe eet = 116
Handling of tritits ht.cy se nttrne vec oe lees aie ae ene eae eee mre 117
Storage: .Vad0 ise SoS oc ee eck cctaee ene coe oe eee 117
Teat Spot) janes areverataehsta. othe Sia ay Noes ate exe LC tae eae eta eae Te 117
tS) 09920 | see ero PS Ra Arians 5 cin ath) cir ce a 140 Gon Oo 117
Cultivation.) Aad csi ets cts) = ies deve anette epee te Te ee 118
(Or yl ee ee ee eine ricer ea at erst a hme ona hha coc iam came 118
istoricallfandaimtroclic toryy-prere reer ote rete rc ncte area arene ea mre 118
Surgical methods... 22% 2 Atyak «cools ensuite dai anes ele ea eeriee cutee 119
2} ct cbiel- eee ae rr ean Cen orcs buat s MAOIs ac cxclda ote Oke 119
Removal of limbs:s=,..cae nik connec eee CE REE een. 119
IRemoyal'ohidiseased oar ke gnrstetey eset tee el ene ar ee 120
Weotind treatments ie 2 hceo mere he cn ere ae 9 120
Wound! disinfection: ster te1tascte ttt aren enn ete 120
Woundiprotectionmcecin ice bette tne Er eee cr eerie ter 120
Woundthealing 5. 20% 5 2 icaeaeo ck sige ube ahaa Reo weenie A este ole 123
Wound corlias.. cst crteatetn tts bic eet ee a eine ne Seen 123
‘Weound wood 24): ueinetice cs Suclsiitaniet relist Sera nal ne Sie ere ee 123
Gailhis'c3 3 ee cit. fap pags chee vee ee Pee SCTE Re ara ae 123
Sprayings ated eds pine nego a eatiskeue epee Ca eA ne eee eee 12
GeneralliGonsiderationss mx ce. came oie cease I ee Eee eee ae ate 12
Orchandmanagement ~.cacter o- ch ceaadcial Ot ee melee eee ene eee 125
Resistantavarileties en cous c cml sigterrsilcneger adie cee she au keeete Nae eraser chen eae eae ce 125
Antenemiyrob bhegpathogenG. nr. .c- cera craven elke eae ee ea ae ten ee eee 126

iBibliographiyyartarewtetscieie Cities ohio Cosa ORCI Lee oR eae ka ete 126

BLACK ROT, LEAF SPOT, AND CANKER OF POMACEOUS
FRUITS!

L. R. HESLER

HOST CONSIDERATIONS
PLANTS CONCERNED

The black rot, leaf spot, and canker of pomaceous fruits is primarily
a disease of the apple, Pyrus Malus L. It affects other trees also, however,
especially the pear (Pyrus communis L.), the quince (Cydonia vulgaris
Pers.), and the crab (Pyrus coronaria L.), showing on these hosts symp-
toms similar to those on the apple. In addition the pathogene infests
the dead parts of a great variety of other trees and shrubs, but in such
cases there is usually no evidence that it has been the causal factor in the
death of the tissues. In the State of New York, at least, this disease
is of economic importance only on apple trees.

VARIETAL SUSCEPTIBILITY
OF FRUIT TO BLACK ROT

The summer varieties of apples are affected by black rot at the time of
ripening, while winter varieties commonly suffer in storage. In Con-
necticut black rot is a most troublesome storage rot (Clinton, r915:5).?

OF FOLIAGE TO LEAF SPOT

Brooks and DeMeritt (1912:183), in New Hampshire, note striking
differences in the varietal resistance of apple seedlings to leaf spot. In
Virginia, Ben Davis and Black Twig are more severely attacked than are
other varieties (Reed, Cooley, and Rogers, 1912:5). Salmon (1907),
writing from England, states that among the varieties most affected
there are Peasgood, Nonsuch, Cox’s Orange, and others. The writer has
noted that Chenango, Baldwin, Rhode Island, and Twenty Ounce show
spotted foliage more commonly in New York than do other varieties.

OF LIMBS TO CANKER

Varieties of apples exhibit a-marked difference in susceptibility to the
disease, and this variation is not the same with respect to the different
parts affected. In western New York Twenty Ounce is the variety most
severely affected by the canker. This variety is rarely found unaffected
by canker, even in orchards that are managed according to improved
methods. Neglected trees of the Twenty Ounce variety are often killed.

1 Also published as Cornell University Agricultural Experiment Station Bulletin 379.
2 Dates in parenthesis refer to bibliography, page 126.

53

54 BULLETIN 379

Paddock (1899 b:181) says that certain growers in New York State have
noted that Twenty Ounce is most likely to be attacked. He lists other
varieties in order of their susceptibility, as follows: Baldwin, Wagener,
Rhode Island, Tompkins King. Regarding the Esopus, Paddock
(1899 b:180) says that this variety has apparently run out because of this
disease. In Ontario, Ben Davis, Northern Spy, and other varieties are
severely injured by the disease (McCready, 1910).

THE DISEASE
NAMES

The disease on the fruit is called black rot, ring rot, blossom-end rot,
and brown rot. The first name is descriptive and definite, and seems
desirable.

Lesions on the foliage are termed leaf spot, brown spot, and frog-eye.

The names apple canker, black rot canker, and New York apple tree
canker, are most commonly applied to the disease when it occurs on the
bark. The term apple canker needs some qualification, since many kinds
of cankers occur on the apple. It was under such an exigency that
Paddock (1899 b: 180, footnote) first used the name New York apple tree
canker. The writer prefers to use this name regardless of its length, not
alone because of priority, but also because of general usage.

HISTORY ;
THE BLACK ROT OF THE FRUIT

The disease on the fruit was observed by Peck (1879:20) in Schoharie
County, New York, and he quotes the remark of stagecoach passengers
that they “never before knew of apples rotting on the tree.” Arthur

(1885) records black rot of quince fruit at Geneva, New York, and notes:

the importance and infectious nature of the disease. Scribner (1890)
notes the disease in New Jersey and describes the symptoms and causal
nature. The same year Baccarini (1890), in Italy, observed the rotting
of otherwise sound apples, pears, and peaches, the decay occurring ina
storeroom of fruit gathered when ripe; this was a new appearance of the
disease in that country. Two years later Halsted (1892) discussed the
black rot of quince in New Jersey. Sturgis (1893, a and b) notes the
disease on quinces in Connecticut in August, 1892, and later (1894)
confirms the work of Halsted. Kinney (1895 c) figures and describes the
disease in Rhode Island. Inthe same year it became an object of control
measures in Kentucky (Garman, 1895). Black rot of apple is reported by
Burrill and Blair (190r) in Illinois; they give a careful description of the
disease and distinguish it from other apple rots. The following year
Clinton (1902), writing from the same station, remarks that the disease on

Brack Rot, Lear Spot, AND CANKER OF PomMAcEOuS FRUITS 55

apples had attracted attention for several years. and that it was known
to have occurred in Illinois at least as early as 1879. The disease as a
storage rot was studied by Lamson (1902) in New Hampshire the same
year. Faurot (1912) describes the disease in Missouri.

W.A. Orton (1904, 1905, 1906, 1907) publishes records of the black rot of
pome fruits, the reports having come to him chiefly from the Middle West.
In 1905 the black rot of quince and pear was especially injurious in Ohio.
Evans (1910) called the attention of the apple growers of South Africa
to the disease, which had just been found on apples at Grahamstown and
also in a consignment of apples from Sidney, Australia. He urged the
importance of excluding the disease from the Transvaal. Recent studies
on black rot have been reported by Wolf (1913) in Alabama.

THE LEAF SPOT

The earliest record which the writer has found concerning the leaf spot
is that by Alwood (1892), who reports brown spot of apple foliage in
Virginia. He had noticed it for several years but states that it was not
serious until 1891, when an outbreak occurred over the State. Kinney
(1895 b) describes the disease in Rhode Island on apple and pear leaves, and
says that it was very common in that State in 1895. Stewart (1896)
reports having found the disease on Long Island in May, 1895; he notes
that it had been observed in 1894 at Westbury, Long Island, by Professor
Beach.. Lamson (1899) lists the disease from New Hampshire and
reports it as having done serious damage in some cases. Corbett (1900)
reports “‘ brown spot,” or “ frog-eye,’’ as common throughout the southern
and eastern counties of West Virginia, and as being more injurious than
either blight or scab. Stewart and Eustace (1902) studied the cause and
control of leaf spot in the eastern United States. The same year Clinton
(1902) notes the severity of the disease in Illinois, and later (Clinton,
1904) he reports its common occurrence in Connecticut. Stone and
Smith (1903) record it as one of the most noticeable diseases of the season
of r902 in Massachusetts. Scott and Quaintance (1907) report the
spotting of apple foliage in the Ozark region, and in the following year
there appeared a more extensive work on the leaf spot problem by Scott
and Rorer (1908). Work on the leaf spot was begun in New Hampshire
in 1908 by I. M. Lewis (1908); this investigation was carried further by
Brooks and DeMeritt (1912), who report it in full. Recent work on the
leaf spot form of this disease has been published in Virginia by Crabill
(1915).

THE CANKER FORM
According to Paddock (1899 b:180), orchardists have been familiar
with this canker disease for years. Attention was first called to the

56 BULLETIN 379

injury by Waite (1898 a), in a paper read at the meeting of the Western
New York Horticultural Society in 1898. In the spring of 1898, Paddock
(1898, a and b, and 1899 a) began investigations which extended through
two seasons. He records having noticed the disease as early as 1891,
and says that it became important about 1895. In 1897, according to
Paddock (1899 b: 192), considerable “twig bight’’ was found at Odessa,
New York.

Mangin (too1) reports the disease in France on branches of apples,
describing its symptoms in order, as he says, to put horticulturists on
guard against invasion of the country by the pathogene. The same year
Chester (1901, a and b), in Delaware, observed what he believed to be
the same disease on apples and pears. His attention had been called to
the canker on the latter host in the spring of 1900, near Smyrna. His
illustrations suggest the possibility that the disease was the super-
ficial bark canker of Edgerton (1908). A few years later Lochhead
(190s) described the disease in Canada. Clinton (1907), writing from
Connecticut, states that his attention was called to a peculiar disease
of apple limbs in the spring of 1906.

Another record of the disease which has appeared from France is that
by Griffon and Maublane (1910). They note very serious injury to
pears in that country, and assert that at the national school of agriculture
the disease was first known in rg08. A study of the disease was taken
up in Canada by Bethune (1909). He reports a great amount of damage
from cankers in the region east of Toronto. The following year a
synopsis of the investigations in the province of Ontario was published
by McCready (1910). A point of interest noted in this paper is that the
great freeze of 1903-1904 in Prince Edward County marked the beginning
of the canker epiphytotic there. The disease has received further attention
in France by Arnaud (1912), who lists it as occurring on a number of

different plants.
GEOGRAPHICAL OCCURRENCE

The disease has a very general distribution throughout the temperate
regions of the globe. Heretofore it has been regarded as a disease peculiar
to eastern and middle western America, but it is now apparent that its
limit is no longer to be so regarded. It has been found in Canada, par-
ticularly in Ontario (Bethune, 1909), Quebec (Lochhead, 1905 and 1909),
and Nova Scotia (Plant Pathology Herb., Cornell University Exsicc.
no. 2657, and Giissow, letter to the writer). It occurs in Europe from
Italy to England, according to the observations of Shear (1913:81-82).
From England Berkeley (1836) reports it on apple fruit, while Salmon
(1907) found it on apple foliage. It is unknown in Norway (Schéyen,
letter to the writer), while both Ravn and Lind (letters) state that it

Brack Rot, LEAF Spot, AND CANKER OF PoMACEOUS- FRUITS 57

is not present in Denmark. From Russia the disease has been reported
by Potebnia (1907 and 1910). Jaczewsky (letter to the writer) states
that the black rot and canker forms occur in the provinces of Kharkof
and Tchernigof, and in the Transcaucasian and Turkestan regions.
Potebnia (letter) has collected all the forms in Kursk, near the city of
Fatej, and states it as his opinion that the disease occurs generally through-
out Russia. Bubak (1909) reports it from Austria-Hungary. It probably
occurs in Switzerland, Germany, and Holland, according to the general
statement of Shear (1913:82). Kirchner (1906: 440) lists it from Germany.
It may not be prevalent there, however, for Hollrung (letter) says the
disease is not well known in Sachsen. Its occurrence in France is reported
by Arnaud (1912) and others. The black rot form has been collected in the
vicinity of Brussels, Belgium, by Bommer and Rousseau (1885). Some
years ago it was introduced into Cape Colony from New South Wales
(Evans, 1910:62, footnote).

So far as the writer has been able to ascertain, the disease is widely
distributed in America. It does not occur, however, so far as indicated
by results from a circular letter sent to the plant pathologists of the state
agricultural experiment stations, in the following States: Arizona, Colorado,
Florida, Idaho, Louisiana, Montana, Nevada, North Dakota, South
Dakota, Tennessee, Utah, Washington, Wyoming, and possibly Oregon.
The canker form is commonest in the East, especially in New York,
while fruit rot seems to occur more frequently in the New England and
. Middle Atlantic sections, although Wilson (1913) reports its occurrence
throughout North America east of the Rocky Mountains. In the Middle
Western States, particularly Ohio and Indiana, the pear and quince,
as well as the apple, appear to have suffered considerably. Quaintance
and Scott (1912) state that the leaf spot occurs in all sections east of the
Rocky Mountains where the apple is grown. In another publication
Scott (1912) asserts that it is found in all humid sections of America.
According to Reed, Cooley, and Rogers (1912:3-4), ‘‘frog-eye”’ is wide-
spread in Virginia. Other States in which the disease occurs are Arkansas,
Connecticut, Illinois, Maryland, Massachusetts, Missouri, Nebraska, New
Hampshire, New York (particularly Long Island), Rhode Island, and
West Virginia (Scott and Rorer, 1908: 48—49).

Probably no apple disease except apple scab is commoner in New York
State than the one here considered. Throughout western New York
the canker form is very prevalent. From replies to a circular letter sent
to fruit growers in various parts of the State, it appears that this disease
is more or less common and serious in all sections, except possibly in the
central eastern part. The fruit and foliage rarely suffer appreciably in
the State, although black rot and leaf spot are not infrequently found.

58 BULLETIN 379

ECONOMIC IMPORTANCE
GENERAL CONSIDERATIONS

The nature of the losses caused by this disease makes very difficult
the possibility of an estimate concerning them. So far as the writer has
found, no reliable data are at hand in regard to this point. The com-
bined injuries produced by the canker, the black rot, and the leaf spot
are doubtless greater than is commonly supposed. It is undoubtedly true
that the New York apple tree canker is often confused with other cankers
by some growers, thus increasing the difficulty of obtaining reliable esti-
mates on the destructiveness of this disease.

It is generally considered that canker is one of the commonest and
most troublesome diseases of the apple, although its destructiveness is
not uniform in different parts of the country. According to Shear (1913:
81-82), the black rot disease of apple is found in Europe from Italy to
England; yet he states that noticeable injury from the disease in orchards
has never been reported. On the other hand, Griffon and Maublanec
(t910:308) state that in France the injury may be very serious. In
contrast to the general situation in Europe, it may be noted that the
damage done by this disease in America is great.

NATURE OF LOSSES

INJURY TO FRUIT. Whenever pome fruits are attacked they are
rendered worthless so far as their market value is concerned. The extent
of injury may be small while the fruit still hangs on the tree, but ultimately
in storage complete destruction is likely to result. Brooks (1909) states
that in New Hampshire the black rot is very common and does con-
siderable damage in cellar storage. Burrill and Blair (1901:2) report
“‘sreat loss at times”’ in Illinois, and Clinton (1902), in the same State,
compares the importance of bitter rot and black rot of apple. The latter
he regards as likely to occur in every orchard to some extent. In Kentucky,
black rot of apples is regarded as the commonest of fruit rots, according
to Garman (1895:127). Stone (letter to the writer) estimates that
in Massachusetts from eighty to ninety per cent of fruit rots is
black rot. Evans (1910) reports a case in which rotting and mummified
pome fruits appeared in a shipment to Cape Colony, and states in this
regard:

During the past three months four hundred and ninety-eight cases of apples and
pears in this condition from Cape Colony have been detained, and in order to safe-
guard the interests of Transvaal fruit growers, the Government, under Government
Notice No. 569, of 18th June, 1908, have warned importers of fruit that all consignments
of pomaceous fruits found infected with this fungus to the extent of one per cent and
upwards will be destroyed upon arrival in this Colony or returned to the consignor.

There is no reason to suppose that this number by any means represents the total
amount of diseased fruit that has reached the Transvaal, to say nothing of the other

parts of South Africa.

Brack Rot, Lear Spot, AND CANKER OF PQMACEOUS FRUITS 59

INJURY TO FOLIAGE. The damage to foliage depends on the extent of
the infection. In the milder cases the injury is not appreciable. In the
more severe cases, partial or even complete defoliation may occur from
six weeks to two months before the ripening of the fruit, as a result of which
the fruit either drops from the tree or remains small and is of poor quality.
In such cases the fruit buds are so weakened as to decrease the possibility
of a crop the following year, and the vitality of the trees is impaired.
Alwood (1892:62) estimates a loss of seventy-five per cent of the foliage
in a part of an old orchard in Virginia, while Stewart (1896) reports a
case of complete defoliation of some trees on Long Island by the first of
July. It is interesting to note, for comparison, that in tg900, in West
Virginia, the disease was regarded by Corbett (1900) as more injurious to
foliage than either blight or scab. Scott and Rorer (1909:10-11) have
observed a case in which, as they believe, the pathogene causing this
disease assisted in the lalling, in late summer, of a large proportion of the
fruit buds of the apple. They state that on Winesaps it would seem
the pathogene alone is capable of killing the buds. Further investigation
is deemed desirable by these writers.

INJURY TO LImMBs. As a rule the canker is confined to the orchard,
although Wilson (1913) says that young nursery stock may be killed.
Bethune (1909:28-29) reports that cankers cause a great amount of
damage in Ontario, Canada. J. W. Eastham (letter to the writer), of
the Ontario Experiment Farm, states that this is the most prevalent
canker in the region east of Toronto, and according to Brooks (1909)
it is the commonest canker in New Hampshire. Warren and McCourt
(1905:341) refer to this form of the disease as causing more loss in Wayne
County, New York, than any other disease except scab. They report
it as very serious in fourteen per cent of the orchards, and as doing con-
siderable damage in nineteen per cent of them. In Niagara County,
New York, Cummings (1909:304) found canker affecting the orchards as
follows: slightly, sixty-one orchards; considerably, sixty-three; seriously,
thirty-seven. Paddock (1899 b: 181, 188) cites a case in which, in an
apple orchard of 80 acres, the trees on 30 acres were ruined and had been
taken out; the trees on the remaining 50 acres were then of little value.

In one apple orchard of three hundred and fifty trees under the writer’s
observation, a count made in August, 1913, showed about thirty-three
per cent of the trees (Baldwin, Hubbardston, and Northern Spy varieties)
with from one to three dead limbs each. On examination of the dead
limbs the New York apple tree canker was found to be present on all.
It was further observed that the pathogene causing the infection had lived
over winter and had spread to such an extent that girdling had resulted
and the foliage had turned yellow and wilted. The fruit on such limbs

60 BULLETIN 379
soon shriveled and was lost. A careful count showed that approximately
ten or twelve barrels of fruit were rendered worthless. The loss here
might be placed at approximately twenty to twenty-five dollars, or about
seven cents a tree. According to the United States Census for 1910,
there were in New York, on the 168,667 farms reporting, 11,248,203 apple
trees of bearing age. On this basis, assuming the losses in the above-
mentioned orchard to be an average, the apparent annual loss would be
about three-fourths of a million dollars for a single season in New York
State. Many cases can be cited in which the infection by New York apple
tree canker is very much more severe, while few orchards in the State,
regardless of their careful management, are entirely free from the disease.
Epiphytotics of this disease, such as have recently been experienced in
the case of the chestnut blight, are of rare or unknown occurrence. It is
characteristic of the disease to take a constant toll year after year, like the
cereal smuts. To the losses so incurred must be added the cost of growing
diseased limbs. In many cases these limbs die, resulting in the cost of their
removal and destruction, which possibly does not seem great in a given
year but is not negligible in the aggregate.

SYMPTOMS
ON THE FRUIT

The disease on the fruit is primarily a ripe rot, but it may appear several
weeks before maturity of the fruit. It may begin anywhere on the surface
or at the blossom end. Frequently the lesions are centered about an
injury such as that caused by insects or hail (Plate vu, 1).

Usually there is only one spot on a fruit. The skin at first becomes
brown in a small area, but later darkens, finally turning black. On green
fruit the affected part may turn black before enlarging to any great extent,
whereas on fruit that is ripe or ripening, the whole may be involved before
it darkens appreciably. Often concentric bands of uniform breadth and
of slightly different shades of color appear about the center of the lesion.
The affected area is distinct from the healthy part, and the diseased tissues
are not of unpleasant taste as in many fruit decays. Later stages in the
development of the rot show a shriveled and much wrinkled surface, which
typically becomes covered with black pustules (Plate vir, 2). These char-
acters may be assumed within a month or in less time. Ultimately a dry
mummy is produced, which may hang to the tree for a year or more.

Black rot has been confused with brown rot and bitter rot, and even with
soft rot. The brown rot disease produces a smooth, coal black, and shiny
mummy, which is much less wrinkled than the black rot mummy. Bitter
rot, in addition to its unpleasant taste, often shows pinkish specks in a

3 Bureau of the Census. Thirteenth Census of the United States taken in the year 1910, 7:195. I913-

Brack Rot, Lear Spot, AND CANKER OF POoMACEOUS FRUITS 6r

localized region near the center of the lesion. The softening of the pulp
in soft rot is not characteristic of black rot specimens. Perhaps the most
distinctive characters of black rot are the long duration of the plumpness
and juiciness of the tissues, and the occurrence of the above-mentioned
black pustules. Under certain conditions the surface of the apple fruit
also becomes studded with white tufts; but these are not commonly
found and are not to be regarded as a diagnostic symptom.

Fruits of the pear and the quince affected with black rot finally become
dry and hard. In storage the peach becomes waxy when affected with
the disease, according to Baccarini (1890:67).

ON THE LEAVES

The foliage of the apple is more frequently attacked than that of the
pear and the quince. The spots usually appear about the time the leaves
open. Alwood (1892:62) notes this date as being about May 1 in Virginia.
He records a second attack which becomes evident about June 20, and a
third outbreak the last of July. Brooks and DeMeritt (1912:181) state
that in New Hampshire apple leaf spot appears soon after the leaves
unfold from the bud. In western New York spotting is more commonly
apparent in July and August. The writer observed spots developed in
September, 1913, at Byron, New York.

The number of lesions that may appear ona single leaf varies from one to
several, and these may be scattered or localized on the surface (Plate vit, 3).
The first evidence of a spot is a minute purple speck, which soon enlarges
until it has reached a diameter of from two to ten millimeters, averaging
about four millimeters. The purplish color is maintained for a con-
siderable time, during which the margin is somewhat indefinite. Later the
lesion is of a yellowish brown color and the spot assumes a more or less
circular shape, while the margin becomes more definite. Still later the
margin becomes elevated and the diseased area sunken. As the spots
grow older they become lobed, due to a secondary extension of the patho-
gene from one or more points, and finally a series of more or less concentric
areas produces an irregular blotch in which the outline of the original
spot can be recognized. The center has now become grayish brown, and
the entire lesion presents an appearance which has given rise to the name
frog-eye.

The spots on the lower surface seem to enlarge as rapidly as those on
the upper, but they are not so conspicuous. Sometimes the center of
the spot on the lower surface is grayish brown. The whole diseased
area may, however, merely appear dark and indefinite.

Frequently small, black, dome-like bodies are found on the upper surface
of the leaf, usually toward the center of the lesion. In severe cases the

62 BULLETIN 379

leaves turn yellow and fall from the tree. According to Brooks and ~
DeMeritt (1912:18r), this leaf fall occurs from six to eight weeks earlier
than would happen normally. Reed, Cooley, and Rogers (1912:3)
maintain that defoliation may occur early enough for a new crop of
leaves to be put forth the same season. Trees robbed of their foliage
from year to year must eventually become greatly reduced in vitality
and finally succumb to a premature death.

Bordeaux injury is sometimes very similar to frog-eye leaf spot; Brooks
and DeMeritt (1912: 190) state that this is especially true if rains follow
the application. Kinney (1895 b) notes also that injuries from the
leaf miner (Tischeria malifoliella Clemens) are sometimes mistaken for
leaf spot.

ON THE LIMBS

In western New York, young spots may be found on the bark at any
time from the last of April until toward the close of the growing season.
Numerous young cankers have been observed on Twenty Ounce trees
in Monroe County orchards during the month of August. It is the
rule that the larger limbs are much more susceptible than the twigs,
and the trunks show comparatively few lesions. The cankers on the
“trunks occur more or less uniformly on the southwest side of trees. The
limbs more commonly show the diseased spots on the upper side. Lesions
are very often found about the base of a small limb or about a wound
in the bark.

In the earlier stages of the formation of a canker, the bark is slightly
sunken (Plates vit, and rx, 4) and reddish brown in color. The diseased
area slowly increases in size and darkens, and, although not conspicuous
at a distance, the spot is readily distinguished from healthy tissue on closer
examination. Some lesions remain very small, measuring only a few centi-
meters in their longer diameter; in such cases the canker usually dies
out at the end of the year. Where the injury is larger, the diseased
spot enlarges from year to year for a distance of a meter or even more.

It is often observed that a canker is merely a superficial roughening
of the bark. In other cases the bark is killed to the wood and becomes
conspicuously cracked (Plate x).

The discolored area may extend over a considerable surface; or, regard-
less of its size, a crevice may appear at the margin, limiting, temporarily
at least, the extent of the lesion. Further spread of the pathogene results
in the formation of a prominent spot, which soon forms a second line
of demarcation between the healthy and the diseased tissue. Repetition
of this process from one or more points at the margin occurs, thus pro-
ducing a lobed appearance (Plate x1, 2); or the spreading may arise from

Brack Rot, LeaF Spot, AND CANKER OF PomMAcEous FRUITS 63

all points about the first marginal crack, so that a series of concentric
crevices is developed, as described for frog-eye of the leaves. The
bark remains closely appressed to the wood for at least a year; later
the dead bark cracks and falls away, exposing the wood and a callus around
the margin of the wound (Plate x, 3).

Cankers that begin to form early in the season show numerous fruit-
ing pustules of the pathogene scattered over the central area of the spot.
These may not become evident, however, until the second season.

Large limbs are rarely girdled the first year; the girdling comes about
by the enlargement of the canker the following season. Complete encircling
results in the death of the parts above the canker, as evidenced by the
yellowing and dropping of the leaves (Plate x1r, 1) and the shriveling of bark
and fruit. It is not uncommon in such cases to find the fruit clinging
to the twigs for a year or more.

Clinton (1907) describes a peculiar type of lesion on apple limbs. He
says, in part:

Another and more peculiar feature of the trouble was the enlargement of the limbs
into somewhat fusiform swellings, as shown in the illustration. In some cases several
of the swellings followed one another on the same limb. These enlargements generally
showed a greater swelling on one side than on the opposite, and often the bark was
split down the more swollen side. Cross and longitudinal sections showed that the
swellings were apparently the result of severe cold, which had injured the limbs unevenly
along the branch, as shown by the blackened wood on the injured portion.

Delacroix (1903 a:135) notes a thickening at the base of some cankers.
This he finds to be a sort of cushion developed in a transverse direction
in the healthy bark. The writer has occasionally observed cankers
showing hypertrophy at the upper and lower ends of the diseased part
(Plate x, 4).

It is to be noted that on quince twigs the cankers are often very indefinite.
A rare specimen is shown in Plate x, 5. The normal color of the bark
is not distinctly lighter than that of the diseased part, so that on this
host the disease doubtless passes unnoticed in many cases.

OTHER ORGANS AFFECTED

A unique case in Virginia of fall blossoming of the apple following
the canker has been described by Reed (1908). This author found normal
blossoms on an apple tree in the orchards of the Virginia Experiment
Station on October 5. The cankers on the limbs had caused the death
of more than half the top of the tree, and many branches, severely affected,
had been able to make a very small amount of growth during the season.
Reed says: ‘‘ It was on such branches as these that fruit buds were found
open on the above named date. Examination of the blossoms showed
that they were normal as regards parts, color, and internal relationships.

64 BULLETIN 379

I am informed by Professor H. L. Price of the Department of Horticulture
of this Experiment Station that this fall blossoming is not uncommon
on trees which are badly affected by the black rot fungus.”

ETIOLOGY
The pathogene here concerned is the fungus Physalospora Cydoniae
Arnaud.

MORPHOLOGY .

PERITHECIA. The perithecia have been found by the writer on the
twigs of apple (Pyrus malus L.) and of witch-hazel (Hamamelis
virginiana L.), and have been described by him in another publication

Fic. 18. PERITHECIUM OF PHYSALOSPORA CYDONIAE
Camera lucida drawing of a median longisection ot a typical perithec1um

(Hesler, 1913:2093). Recently the writer has found the ascogenous form
on twigs of white oak (Quercus alba L.).

The perithecia are usually scattered, standing separate from one another.
Sometimes, however, from two to four fruit bodies are joined together,
but no stroma has ever been observed. They are buried in the cortical
tissues, protruding at maturity by a short, papillate ostiole. Their
form is globose to subglobose, measuring from 180 to 324 in the vertical
diameter by 300 to 4oou in the horizontal diameter, averaging about
225 by 325un.

A typical perithecium is shown in figure 18. The wall is differentiated
into two layers. The thickness of the outer layer varies slightly with
the sides and base of the perithecium, and the pseudo-cells are thick-

BULLETIN 379 PLATE VII

SYMPTOMS OF THE DISEASE ON FRUIT AND FOLIAGE

1. Types of infection on apples, early stages
2. Apples reduced to mummies ult of the disease
Types of infection on apple leaves as commonly found in New York State

BULLETIN 379 PLATE VIII

INOCULATION EXPERIMENTS ON APPLE

_ The specimen on the left is a check; the next three show cankers resulting from infections by ascospores from apple; the specimen on the right was
inoculated with ascospores from witch-hazel, and in this case infection did not occur. Date of inoculation, July 16, 1913; photograph made September

20, 1913

BULLETIN 379 5 eTbNGD} IDS

NATURAL CANKERS AND CANKERS PRODUCED BY ARTIFICIAL INOCULATION WITH
PHYSALOSPORA CYDONIAE

1. Natural infection on the left; artificial infection on the right. The latter inoculated on July 1,
1913, with a strain from Twenty Ounce apple bark. Photograph made September 30, 1013

2. Canker on trunk of mature pear tree. Inoculation made July 18, 1910, photograph made
September I, 1911

3. The result of inoculation by use of pycnospores from apple leaves. The healing process has
occluded the wound before the pathogene could produce a large canker. Inoculation made July 1,
1912, photograph made September 20, 1913

4. Canker on Baldwin twig produced artificially, using ascospores from apple. Inoculation made
July 25, 1914, photograph made December 10, 1914

BULLETIN 379

Ts
o
3:
4.
5

SYMPTOMS OF THE NEW YORK APPLE TREE CANKER

Typical old and much-roughened canker on Twenty Ounce apple. The bark is still clinging

Old canker on apple, showing roughened surface. Some of the bark has fallen from the lesion

Old canker on apple, showing callus about the margin. Note that most of the bark has sloughed off
Cankered limb of apple, showing hypertrophy toward the upper end of the lesion

Canker on quince

«s

BULLETIN 379 PLATE XI

INOCULATION EXPERIMENTS WITH PHYSALOSPORA CYDONIAE

1. The three cankers on the left produced by inoculating pear with ascospores fram apple.
Check on the right. Inoculations made June 6, 1913, photograph made September 20, 1013

2. Canker on Twenty Ounce limb produced artificially, using pycnospores from apple.
Inoculation made June 20, 1912, photograph made September 20, 1913

3. Canker produced on pear by inoculation with ascospores from apple.
of pycnidia should be noted. Inoculation made June 6, 1913, photograph made Gestenibes
20, 1913

BULLETIN 379 PLATE XII

a

NEW YORK APPLE TREE CANKER

1. Twenty Ounce apple tree, some of the larger limbs of which have been girdled by the fungus.
Jence that this has occurred is found in the defoliated tops of affected limbs

2. External view at left, and internal view at right, of young black rot lesions on apple; the specimen
on the right shows the tissues involved

i

BULLETIN 379 PLATE XIII

ee am 7

VARIOUS STAGES OF PHYSALOSPORA CYDONIAE

1. Showing differences in growth on nutrient azar from pycnospores (heavy dark growth on left)
and from ascospores (scant growth on right)

2. Photomicrograph of asci, ascospores, and paraphyses from a single perithecium

3- Sclerotia as they appear in pure culture

4. Twig of apple, showing dark masses of pycnospores which have oozed from the pyenidia when
the twig was kept in a moist chamber

BULLETIN 379 PLATE XIV

INOCULATION EXPERIMENTS WITH PHYSALOSPORA CYDONIA®
Inoculation made July 1, 1912, using pycnospores
Photograph made September 20, 1913
Specimen shown on left inoculated
Specimen shown in center inoculated with pycnospores from
The very slight infection should be noted. Check on right.
Inoculation made June 6, 1913, photograph made September 20, 1913

1. Canker on right, check on left.
from pear, the fungus having followed fire blight.
2. Comparison of two different apple strains on pear.
with ascospores from apple.
apple, following fire blight.

Brack Rot, LEAF Spot, AND CANKER OF PoMACcEOUS FRUITS 65

walled. The inner, thin-walled layer is of very uniform diameter. In
cases in which the perithecium is depressed, the outer layer is reduced

at the base and is from one to three pseudo-cells in
thickness, whereas the lateral outer walls are from two
to five layers of pseudo-cells in thickness.
appears as a narrow passage in the papilla, the walls
of which show the same distinct layers as those just
described for the sides and base of the perithecium.
The asci, with the interspersed paraphyses, usually fill
the cavity of the perithecium. Arnaud (1912:11) states
that in general the paraphyses are formed by rows of

1)

FIG. 20. ASCI OF PHYSALOSPORA CYDONIAE FROM

DIFFERENT HOSTS

The upper series represents variations as found on apple
bark. The lower series shows variations from b:

hazel

The ostiole

cells which
in the ma-
ture peri-
thecium

Fic. 19. ASCI AND
are sepa- PARAPHYSES OF
rated one PHYSALOSPORA

CYDONIAE

from an- Camera lucida draw-
: ing of ascl and paraph-
ot h er mM yses, showing structure

of the latter and typical
the form of arrangement of asco-

distinct fil- spores in the ascus

aments. He says that in cer-
tain cases, however, the
paraphyses remain aggluti-
nated by their walls and
appear in section like rows of
cellular cavities, as in Cucur-
bitaria (C. Spartii and other
species). He explains that if
the rows of cells are not very
numerous the existence of the
paraphyses may become un-
certain. Arnaud finds this
the case with Physalospora
Cydoniae. The writer, how-
ever, has not observed this
condition of the paraphyses;
to him they appear distinct

ark of witch- and non-septate (Fig. 19).

The asci are abundant;

asci crushed from one perithecium are shown in Plate xm, 2. They are
usually clavate, although they sometimes tend to be cylindrical, measuring

66 BULLETIN 379

from 21 to 32 by 130 to180 yu. The tip of the ascus is thickened, but a
complete canal from the inner wall to the outside has not been observed;
only a suggestion of such a canal
has been seen even after the peri-
thecia had been kept in a moist
chamber for several hours. Varia-
tions of asci from different hosts are
shown in figure 20.

The ascospores are ellipsoidal, or
often inequilateral (Fig. 21); they
measure from 10.8 to 15.2 by 23.4
to 34.2, averaging 11.5 by 28uy.
They are hyaline to greenish yellow.
Under ordinary conditions the spores

\:t:| show a very thin gelatinous sheath,

~ \Y but after they have been in a satu-

: rated atmosphere for a few hours the

B ‘ sheath becomes very broad and evi-
FIG. 21. TYPES OF ASCOSPORES OF PHy- dent. The arrangement of the spores

SALOSPORA CYDONIAE 5 a : i
A, Typical mature ascospores as found in nature; in the ascus is more or less biseriate.

the gelatinous sheath; Goold ascospores, showing The paraphyses are distinct and are
Pee eee occasionally branched near the tip.
Not infrequently the apex shows a tendency to be clavate.

The number of spores in each ascus is typically eight, but exceptions
have been found in the fungus on apple twigs. The variation ranges from
two to eight spores within an ascus, all intervening numbers having been
observed. Four-spored asci are not uncommon (Fig. 20). The contents
of ascospores are either densely granular, or vacuolate and oily. Two
guttules are occasionally found.

pycnipia. The morphology of the pycnidial form of this fungus is
variable (Fig. 22). The pycnidia are situated in the cortical tissues
and are usually scattered and distinct, although on the same organ of
the host they may be single, confluent, or united into a stroma. The
number of pycnidia per unit of area is usually less on woody substrata
than on fruits; on apple fruit there may be from one hundred and twenty

_to one hundred and fifty pycnidia per square centimeter.

The typical simple pycnidium (Fig. 22, A) measures from 200 to 300 u
in each diameter, whereas the compound fruit body may vary from 200
to 460 u in the vertical diameter and from 200 to 720 in the horizontal
diameter (Fig. 22,G). Their shape is in general the same as that of the
perithecia, globose to subglobose, and they have the same distinct outer
and inner walls. The thickness of the entire pycnidial wall is variable,

Brack Rot, LEAF Spot, AND CANKER OF PoMACEOUS FRUITS 67

as in the case of the perithecium. The basal part is thinner in the case
of the subglobose fruit bodies. This condition may be attributed to the
fact that less protection is needed at the base; or perhaps here the thick-
ness may be partially determined by mechanical pressure brought about
by the resistance offered by the host tissue.

Arising from the inner thin-walled cells are the pycnosporophores, which

FiG. 22. VARIATIONS OF PYCNIDIA OF PHYSALOSPORA CYDONIAE

A, Typical simple unilocular pycnidium; B, pycnidium with long neck, similar to C but with an ostiolum;
C, pyenidium similar to B, ostiolum not yet developed; D, pycnidium from apple leaf; E, hair-like out-
growths on the tip of an ostiolum, developed under moist conditions; F, pycnidium with mound-like struc-

ture at base; G, pycnidium which approaches in appearance the fruiting body of species belonging to the
form-genus Botryodiplodia F

extend entad. They are clavate, flask-shaped, or cylindrical. They may
be as long as the spore itself, from 25 to 30m, or may measure less than
8; the average dimensions are from 10 to 15 w by 3 to 4p. At the tip
of each is developed a pycnospore.

In some cases there is a mound-like structure at the base of the pycnidium
(Fig.22,F). This is illustrated by Duggar (1909:353, fig.171). Ithasbeen
a matter of conjecture whether this may appear only in an oblique tan-

68 BULLETIN 379

gential section, or whether it is a bilocular tendency. It does not seem
possible that any such structure would appear merely in a section that
was not cut vertically. If this were true, the question would then arise
as to whether this same appearance would not extend at all points along
the lining of the cavity, and hence merely make the wall thicker rather
than give it the aspect just described. It seems, therefore, to be a
bilocular tendency.

Frequently the pycnidium approaches and even reaches the condition
characteristic of the form-genus Botryodiplodia (Fig. 22, c). The sporog-
enous layer extends inward at places, giving the inner wall a corrugated
appearance. This condition is found in nature and has been developed
in culture from spores in pycnidia which originally did not show this
structure. The simplest condition suggesting the form-genus Botryodi-
plodia is found when a single mound-like structure occurs at the base of
the pycnidium, as previously described (Fig. 22, Fr). Frequently this finds
its expression in the form of a bilocular condition, which is a step nearer
the Botryodiplodia type.

The ostiolum offers some interesting variations. Miss Walker (1908)
describes a form which she believes lacks an ostiolum. In the place of
the typical conical ostiolate neck there was found a much-thickened wall
at the apex of the fruiting body, and the papilla itself appeared longer
than usual. The writer has cultured the ostiolate form from an apple,
and has obtained, on various agars and on apple fruit, pycnidia having
the characteristics described by Miss Walker (Fig. 22, c). The evidence at
hand indicates that a pore may or may not be present, depending some-
what on the time of year and on weather conditions. In any case an
ostiolum will ultimately be developed (Fig. 22, A,B, D). Brooks and De
Meritt (r912: 184) report three types of pycnidia but all forms are ostiolate.
It does not seem likely that any strain will remain void of an ostiolum
throughout its history. A strongly papillate form similar to that shown
in figure 22, c, but with an ostiole developed, is illustrated in figure 22, x.
A form of the fungus which at first appeared to have a non-erumpent
pycnidium was found in apple bark and twigs of Celastrus scandens L.
After the material had been in a moist chamber for a few days, however,
the pycnidia broke through the epidermis.

In conclusion it may be stated that the pycnidia may vary in mor-
phology on different host plants, yet this variation is no greater than that
on the same host plant.

PYCNIDIAL FORMATION. ‘The pycnidia arise from the mycelium and are
found abundantly on cankers and decayed fruit. Also they may be
produced on various artificial media. They occur sparingly on spotted
leaves.

Brack Rot, Lear Spot, AND CANKER OF PomaceEous Fruits 69

So far as has been determined, the process of formation is similar on
different substrata. The earlier stages are more accurately followed
in agar cultures than on any organs of the host plant. The writer’s obser-
vations have been made by examining petri-dish cultures under the low
power of the microscope and by the use of prepared slides from such
cultures. The material was prepared as follows: Pycnospores or hyphal
threads were planted in the center of agar plates, and, as the hyphe
developed, pycnidia appeared in more or less definite concentric rings.
In this way the oldest pycnidia were nearest the starting point, whereas
the youngest were found near the margin of the culture, the stages between

Fic. 23. DEVELOPMENTAL STAGES OF THE PYCNIDIUM

A, Early stage in pycnidial development. The hyphe have become closely septate, are broadened,
and are beginning to tangle. B, Early stage in the process, showing the origin of hyphe which enter
into the pycnidium. Some come from adjacent hyphz, others arise from cells of the threads in the
immediate tangle. C, Early stage. Branching of hypha, preliminary to coiling and twisting as in D
and F. D, Early stage. Twisting of hyphe about one another. E, Early stage, showing symohyo-
genetic and meristematic tendencies in pycnidial formation. F, G, H, More advanced stages in the
process of pycnidial formation

the two being intermediate. Blocks of agar were cut out from the dish,
fixed, and imbedded in paraffin. A single section frequently includes
a gradual series of the several stages, from the very youngest to the more
mature structures. The sections were made both perpendicular and
parallel to the surface of the agar, the second method proving the more
satisfactory. ’

The young pycnidium as it occurs in agar appears to be made up of
a closely tangled mass of hyphe. In section the young fruiting body
is composed of pseudoparenchyma, the cells of which are closely packed
and consequently somewhat angular (Fig. 23, H). Asis noted by De Bary
(1887:247), pycnidia may arise either as intercalary formations on hyphal
branches by the swelling and division of cells, or by the union and inter-

70 BULLETIN 379

weaving of mycelial threads. The former process is termed meristogenetic
and the latter symphyogenetic. A third possible method, not unknown
among the fungi, is by a combination of these two processes.

Potebnia (1910:62), in a note on Sphaeropsis pseudodiplodia (Fck1.)
G. Del., states that the pycnidia arise meristogenetically. The writer
was for some time under the impression that this was the character of
the process, but this opinion was based on observations of later stages
rather than on the earliest steps in the development. The dense pseudo-
parenchyma of the maturer fruit bodies suggests meristematic divisions,
but apparently the structure, for the most part, arises symphyo-
genetically (Fig. 22).

In agar cultures a group of threads may be observed to be directed
toward a common point where the pycnidium is to be formed. Here
the hyphz are composed of cells from 6 to 7 w broad, their length varying
from 20 to 7ou, always longer than broad. .In the region where the
pyenidium is to be developed, the cells become noticeably shorter by
the laying down of new walls; the cells also increase in diameter by
growth, and the hyphz increase their numbers by branching (Fig. 23,4).
This stage is observed with ease in petri-dish cultures.

The behavior of the threads in the formation of the pseudoparenchyma
is varied and the process is somewhat indefinite. The mycelial branches
that enter into the structure may arise from the short cells (Fig. 23, a), or
they may grow in from adjacent hyphe (Fig. 23, £). The interspaces
found in the earlier stages are filled by the growing in of these branches
and by a budding-like action of the hyphal cells bordering the space
(Fig. 23, B).

Serial sections show that there is considerable coiling and gnarling
of hyphe. Threads may twist about one another for some distance
in a rope-like fashion (Fig. 23, D). In some cases the threads are localized
in their intertwining so that the resulting structure becomes a knot or
ball of densely woven hyphe (Fig. 23, F, G, H). The formation of sucha
structure necessitates that the hyphze pass into many planes, and in cross
sections the ends of many hyphze present a pseudoparenchymatous appear-
ance (Fig. 23, H).

In the intertwining process, hyphe may conjugate in an H-shaped
fashion. In some cases threads that are parallel probably fuse side by side,
although the evidence for this is not complete.

The next important stage is the formation of the cavity. At first
no differentiation of the closely tangled mass of threads is shown in the
young pycnidium, but soon the preparation for the cavity is evident.
Certain cells occupying the central region become more densely granular
than the surrounding cells. This appears to be the beginning of the

Brack Rot, Lear Spot, AND CANKER OF PomMacEous FRuITS 71

cavity. Later stages show the breaking down of these cells, and finally
an oval or a globose cavity is formed. Baccarini (1890:69) states that
these central cells transform by a mucilaginous process, and that the
cavity is enlarged by the gelatinous center’s absorbing water and exerting
a pressure on the sporogenous layer. He emphasizes the importance
of the central “tissue” and expresses the opinion that it has a special
function, believing that it is destined to become sporogenous whereas
the outer surrounding cortex only furnishes nourishment to these cells.

The formation of the ostiole is similar to the process exhibited by the
development of the cavity. The cells break down, enlarging the passage,
and finally the wall is definite and continuous with that of the spore cavity.

The spore-bearing area occupies almost all the space not included
by the ostiole. The cells lining the cavity
arch outward, and continued growth results
in the formation of a stalk. The tip of the
stalk swells, and ultimately a mature spore is
cut off (Fig. 24). The further development
of the pycnospores has been discussed.

pycnosporEs. The morphology of the F!- 24- yew aren go DIN ADEN
pyenospores has been more carefully studied gtages in the formationof a pyeno-
than that of the pycnidia. In the same and ‘?%°!0™ 4 conidiophore
in different pycnidia on the same and on different plants, wide variation
with respect to size, color, shape, and,.septation have been observed
(Fig. 25). ;

The average mature pycnospore measures about 12 by 25 yu, although
the range in single or in different pycnidia on the same or on different
hosts or host parts may be considerable. From the measurement of
hundreds of pyenospores, it has been found that they range from 7 to
16.2 broad by from 16 to 364 long, while the averages from different
hosts range from 9.5 to 13.3 by 19.8 to 27.8u. Spores on the apple
show a slight variation on the different organs, as follows: on the fruit,
10.6 by 254; on the twigs, 11.6 by 23.8; on large limbs, 12.9 by 24.9;
on the foliage, 12.3 by 23.5u. Paddock (1899b:195, table 1) notes
considerable variability with respect to size as the spores occur on
different plants, but he says: “‘ Yet the spores produced on apple fruits
inoculated with cultures from either host, are of the same size and
character; similarly, though not shown in the table, when pear trees are
inoculated with cultures of Sphaeropsis taken from apple trees the result-
ing pycnidia and spores are of the average size of those found in nature
on pear tree bark.”

. The mature pycnospores are brownish, varying from a very light to a
dark ferruginous color. The color darkens with age, so that the very
youngest mature spores are hyaline. The question of the maturity of

72 BULLETIN 379

these colorless spores has frequently arisen. The writer has germinated
them, and is of the opinion that they should be regarded as physiologically
mature. The hyaline color is replaced later by a yellowish green tinge,
and finally a brown of varying density is assumed, the spore becoming
very dark brown in the final condition of coloration, as noted above.

\OOl say sane
90) 08 cae is ASD

Fic. 25. VARIATIONS AND TYPES OF PYCNOSPORES OF PHYSALOSPORA CYDONIAE FROM
VARIOUS HOSTS

A, Typical unicellular pycnospores; B, typical bicellular pycnospores; C, three- and four-celled pycno-
spores, not common; D, pycnospores from apple twig; E, pycnospores from apple limb; F, pycnospores
from a single pycnidium, from apple twig; G, very old pycnospores which have burst; H, pycnospores
from apple fruit; I, pycnospores from sumac; J, pycnospores from sumac showing peculiar fusion; K,
pycnospores from sumac; L, pycnospores from crab; M, pycnospores from mulberry; N, pycnospores from
rose fruits; O, pycnospores from bittersweet; P, pycnospores from rose of sharon; Q, pycnospores from
witch- hazel; R, pyenospores from spicebush

Ae!

The several shades of color may be represented by the spores of a single
pyecnidium, although the majority are uniform in this respect.

The typical pycnospore is ellipsoidal, frequently tapering slightly
toward the basal end (Fig. 25, A). The shape also is a variable character,
however. Pyriform spores may accompany ellipsoidal, globose, or some-
what elongated forms.

Brack Rot, LEAF Spot, AND CANKER OF PoMACEOUS FRUITS 73

The question of septation of pycnospores is of importance because of
the fact that it involves the systematic value of the character, or varia-
tion if it be so called, in separating the form-genera Sphaeropsis and
Diplodia, and because of the physiological significance of its formation.
In nature, three possible conditions exist with respect to the presence
of one- and two-celled spores. A pycnidium may contain only one-celled
spores (Fig. 25,A) or only two-celled forms (Fig. 25, B), or both kinds may
be present (Fig. 25,E,P,Q,R). Occasionally three-celled and even four-celled
pycnospores have been observed (Fig. 25, c). It is a striking feature in
this regard that no strain has come under the writer’s observation that will
not produce two-celled spores. Just what factors induce cross-wall for-
mation is a matter not well understood. Mature unicellular spores placed
to germinate, whether germinating at once or not, will sometimes develop
aseptum. Again, spores that are found scattered about on the bark of the
host plant show the bicellular condition. In very dark spores the cross-
wall is not always readily visible and may be easily overlooked.

The writer made observations on several strains regarding this character.
Spores were placed in a drop of water and set in a moist chamber for several
hours. At the beginning and at the end of each experiment the spores
were examined for septation. The strains when collected, with the
exception of one (no. 64)! on mulberry (Morus alba L.), possessed one-celled
spores only. After being placed to germinate, or in nature after they had
oozed forth on the substratum, septa began to appear and the percentages
were as follows: one-celled spores, from two to ninety-five per cent;
two-celled spores, from five to ninety-eight per cent; three- and four-
celled forms, rare. The average for all such observations shows that the
percentage of one- and two-celled forms is about equal.

Cultural studies were made of an apple strain (no. 82) with reference
to this and other morphological characters. A single ellipsoidal, brown,
one-celled pycnospore, 10.8 by 21 in size, from a pyenidium in which
all the spores were one-celled and typically like the one described, was
isolated on March 3, 1913, and a pure culture was developed from it.
Examination of the culture at intervals showed the development of
hyaline, Macrophoma-like spores. At the end of twenty-four days these
had become brownish, and, while the majority were ellipsoidal, averaging
from 9 to 10 by 21 to 22, a few were pyriform and measured 12.6 by
30.6u. At the end of fifty days an occasional spore was found with a
cross-wall; after eighty days thirty per cent of the spores were two-celled,
and on May 27 sixty per cent were bicellular.

From the same culture a second generation was originated by culturing
a one-celled, ellipsoidal, brown spore, 11 by 22 1n size. The following

4 The specimens were numbered consecutively regardless of source, host, and other considerations.

74 BULLETIN 379

notes were taken: Within two weeks an occasional spore measured 7.5
by 214, although the usual size was from 9 to 10.8 by 19.8 to 26.1 yu.
After forty days several two-celled spores appeared. At the end of two
months, fiftv per cent of the spores were one-septate.

A third generation was initiated by planting a spore from the second
generation, of the same shape and measurement as the preceding. After
one month twenty-five per cent of the pycnospores were of the Diplodia
type. i

Another series was studied, using a two-celled spore from a pycnidium
in which both one-celled and two-celled forms were present. Within one
generation a single spore, 10.8 by 21 in size, two-celled, brown, ellip-
soidal, had developed offspring showing the usual color variations — that
is, from hyaline to greenish, and finally brownish. After eighteen days
some of the spores measured 12 by 28 pw, the average being 10.5 by 21.
Septation began to show after five weeks, and within eighty days sixty
per cent of the spores examined were two-celled.

Apparently, from a single pycnidium in which the spores are of a given
type there may develop in succeeding generations a wide variation in size,
color, shape, and septation. In an early stage the Macrophoma type may
appear in both size and color; later the Eu-Sphaeropsis type, one-celled,
brown; and finally the Diplodia forms. The variable shapes that may be
found in the generations succeeding a given type indicate that two-celled
forms may be mere deviations in the life cycle. On the other hand, Brooks
and DeMeritt (1912:184) report from New Hampshire a large-spored
form which holds true to its morphological characteristics for several
generations.

Markings on the wall of the pycnospores are reported by Griffon
and Maublane (1910:312). These authors claim to have discovered an
undescribed character of the spores of this species, namely, a shagreened
wall. This character is not reported elsewhere in literature, and has not
been observed by the writer among the several strains studied, including
Dr. Peck’s type specimens of Sphaeropsis Malorum Peck.®

Long, slender bodies, measuring about 1.54 in diameter and often
50m in length, have been observed interspersed between the pycnospores
of a strain from apple twigs. They are not of frequent occurrence in the
experience of the writer.

MycELIUM. The mycelium is composed of septate tubes, monopodially
branched and comparatively broad — being on an average about 4 to
7 in diameter. In the young hyphe cross-walls are rare, but in older
branches the threads are often short and frequently with bulging lateral

5 Following the Vienna Code published in 1906 (Wettstein, R. von, Wiesner, J., and Zahlbruckner, A.,
Verhandlungen des Internationalen Botanischen Kongresses in Wien, 1905, p. 200), this specific name should
be capitalized.

Brack Rot, LEAF Spot, AND CANKER OF PoMAcEOUS FRUITS 75

walls. Color is lacking in young aérial threads, but as age increases a
greenish yellow, then bluish green, brown, and finally dark brown, hue is
assumed. In mass the mycelium ap-

pears black. In cultures lacking potas- ———é

sium a violet tinge has been observed.
The walls of the hyphe are relatively yy
thick, and sometimes a decided double
contour of the membrane is visible.
The appearance of the cell contents

1)
& LA

om

ae |e
iat
Ren.
ae

Ry
“o
S\
wy
i}

Fic. 26. PART OF CROSS SECTION
OF SCLEROTIUM

varies, apparently depending
somewhat on age and nutri-
tion. Young and well-nourished
cells are densely granular, while
older threads contain vacuoles
and glycogen drops in abun-
dance.

SCLEROTIA (Plate xu, 3,
and Fig. 26). Sclerotial bodies
have been found in nutrient
media of high sugar content
and in oat agar cultures of
ascospores from Hamamelis
virginiana. Walker (1908:38)
reports the development of
sclerotium-like bodies resem-
bling pycnidia on artificial

media. They have also been ob-

Fic. 27. CHLAMYDOSPORES OF PHYSALOSPORA served by Baccarini (1890 : 67)
CYDONIAE =

Types of chlamydospores found in pure cultures

just under the skin of the
apple.

CHLAMYDOSPoRES (Fig. 27). Chlamydospores have doubtfully been
observed by the writer in host tissues. In a few cases a suggestion of

76 BULLETIN 379

such a body was found in apple bark. In old cultures on various artificial
media, large, thick-walled, intercalary, brown, spore-like bodies are some-
times present in abundance. They were also obtained easily by transferring
bits of mycelium to sterile water. They have been observed in agar cul-
tures that have become contaminated by bacteria, being found more
especially near the bacterial colonies. The most striking forms observed
were on old agar cultures of the strain (no. 6) from Rhus typhina L.
Similar bodies are described and figured by Hedges and Tenny (1912: 16)
in their studies on Sphaeropsis tumefaciens. These large bodies suggest
young pycnidia, owing to the form and cellular structure. All gradations
from thick-walled, colorless, greenish or brownish, granular, swollen cells,
occurring singly or in chains, are very common in artificial culture.
These bodies have been germinated by the writer, the germ tubes de-
veloping into hyphe of the usual type (Fig. 27, near top).

MICROCONIDIA (Fig. 28). Microconidia, or secondary bud-like bodies,
have been observed in culture after forty-eight hours. They develop
as swellings near the tips of the growing hyphe. They
are globose or somewhat pyriform, measuring from 3.6
to 6.3m by 7 to 14.5, averaging 4 by 9.5 p.

YEAST FORMS. Alwood (1898b) records the dis-
covery of a yeast form occurring in the laboratory
cultures of the fungus, which on isolation and rein-
oculation of apple fruit produced its fruiting bodies.
Such forms have never occurred in any of the writer’s
J pure cultures.

Fic. 28. microco- ‘The variations exhibited by this fungus do not repre-
NOsPORA CYboMEaw Sent unique phenomena among the fungi. Shear and

Showing microconidia Wood (1913:63) say of Glomerella: “‘No character,

developedonthemycelial _. : Ascent
threads, ‘The three mi- Cither morphological or physiological, seems to be well

Sa Soe ee einer nabCoah They find (page 64 of same reference) wide
SHES variability in the manner of conidial production; all
intergradations between a hyphomycetous type and a distinct melan-
coniaceous type of structure occur in cultures. Seta may be present in
some cultures and absent in others, while paraphyses are regarded as of
little taxonomic value. Duggar (1909: 303), in speaking of the Alternaria-
Macrosporium question, says: “‘ The catenulate method of spore produc-
tion has been reported only in artificial cultures in this case, and it is
possible, furthermore, to obtain for various fungi in such cultures in
general many variations from what would be considered the normal type
of spore production upon the host.”’ It is stated in the same place that
cultures of such forms as Fusarium, Gloeosporium, and Cercospora yield
variable characters in culture. Seaver (1908) points out the misleading

—

Brack Rot, Lear Spot, AND CANKER oF Pomaceous FRUvITS vie
and misused color characters in some of the Hypocreales. Stevens and
Hal! (1909 b) report considerable variation in certain forms under different
environmental influences.

PHYSIOLOGY

METHODS OF ISOLATION. The chief methods used in isolating the
organism were: the plating of spores in agar and the transfer of single
germinating spores; transfer of single spores by the capillary tube method
as described previously by the writer (r913:291-292); planting bits
of diseased tissue in agar plates. The first two methods are advanta-
geous in getting pure lines or races. The third method has practical
advantages in its simplicity and the ease with which the culture is obtained.

CULTURAL CHARACTERS — GENERAL. The ability of this fungus to
grow on the commonly used culture media is a noticeable physiological
character. It is easily isolated, and its appearance in successive stages
of development is generally the same in all the culture media employed.
The colonies are at first cottony; after from two to five days the sub-
merged threads are green or blue-green for about a week, after which
the growth is dark or nearly black, but almost without exception the
outer ends of the aérial threads maintain their original cottony appear-
ance. After from seven to ten days pycnidia appear. The writer has
always been able to develop pycnidia in culture, although Brooks and
DeMeritt (1912:183) found considerable difficulty in getting cultures to
sporulate. Often a distinct concentric zonation occurs in plate and tube
cultures. The exudation in culture of drops of liquid has been observed
frequently. This is described by Potebnia (1907), who regards it as an
excretion product.

The general characters described’ above — except zonation, which is
irregular in its occurrence — apply to the following media: several dif-
ferent agars, including potato, prune, apple, oat, bean, and nutrient; solid
vegetable substances, such as potato cylinders, bean pods, apple twigs,
and apple fruit cylinders; synthetic liquid media, such as Fraenkel and
Voge’s, Cohn’s, Rankin’s, and Uschinsky’s solutions.

CULTURAL CHARACTERS — SPECIAL. The writer (1913:292-293) has
previously reported differences in the growth of cultures from ascospores
and pycnospores when planted in +1o nutrient agar. On the one hand
pycnospores were developed within about one week from pycnospore
plantings, whereas on the other hand no fruiting bodies had appeared
after several weeks in cultures from ascospores, the growth remaining
stunted. Cultures of ascospores and of pycnospores were similar on other
media (Plate xmt, 1).

PROTOPLASMIC STREAMING. Protoplasmic streaming in the hyphz
has been studied by Potebnia (1907). He has found that movement

78 BULLETIN 379

begins with the germination of the pycnospore. The direction is first
toward the tip, some granules moving more rapidly than others. On
reaching the tip, those that have moved the faster direct their movement
backward, in some cases forming groups. The streaming is not dependent
either on evaporation through aérial parts or on the structure of the
protoplasm, but is conditioned only by apical growth of the hyphe and
by inner processes. The slow movement is pulsative, and it is observed
that increased temperature accelerates forward movement and cooling
often induces backward flow. It issuggested that the streaming is similar
to the slow movement observed by Van Tieghem in the hyphe of the
Mucorales. :

PATHOGENICITY

The ability of the organism to produce the disease, particularly the
leaf spot and canker forms, has been a matter of no little consideration.
The difficulties that are met in attempting to infect various plants have
brought out, not only some conflicting results, but also, what is more
encouraging, some interesting problems with reference to the causal
agent and the taxonomic relationship of the so-called species on the
different host plants. The cross-infection of the several hosts, and the
role of organisms associated with Physalospora Cydontae in the production
of the lesions, are points that have a practical and scientific bearing on
the whole problem. The different forms of the disease are followed
in the succeeding discussion.

BLACK ROT OF APPLE. The ability of the fungus to cause decay of
fruits was established, after a fashion, in 1878 by Peck, who writes
(1879:20) that “the disease is contagious, and may be communicated
from one apple to another.”

Von Thttmen (1879) °® regards the fungus, which he called Dzplodia
Malorum Fckl., as a saprophyte rather than a parasite, but believes that
it is capable of attacking sound fruit and is able to cause notable injury
in storage. :

Arthur (1885) inoculated sound quinces by inserting beneath the skin
a bit of diseased fruit tissue containing spores of the fungus (which he
calls Sphaeropsis Cydoniae C. & E.). The inoculated fruits were placed
under a bell jar. Arthur says: ‘‘ The spores germinated, and the rotting
progressed slowly, when, on the twenty-second day, the spot had reached
aninch and a half in diameter, and the fruiting points had begun to appear.”

Halsted (1892) states that the fungus grows interchangeably on apple,
quince, and pear fruits. He reports having corroborated his laboratory
experiments by field observations.

6 Original not seen by the writer; context taken from Baccarini (1890: 70).

Brack Rot, Lear Spot, AND CANKER OF PomacrEous Fruits 79

Sturgis (1894) made inoculations both in the field and in the laboratory,
confirming the work of Halsted (1892) and showing that when the skin
was not broken previous to inoculation the fruits remained in a sound
condition.

Paddock (1899 b:185) produced black rot of apple artificially within
a few hours by the use of the black-spored fungus, pycnidia appearing
after sixteen days. Again, Paddock states (page 193 of same reference)
that the fungus from pear, quince, and Japanese plum produces rot in
apple, pear, and quince, if the skin is punctured and moisture is furnished.

More recent inoculation experiments are reported by Walker (1908),
Morse (1909), Arnaud (1912), and others.

Two forms of Sphaeropsis were observed by Walker (1908), both of
which were capable of producing black rot — the newer form, however,
being a more vigorous rot producer. The morphological differences
have been previously noted.

The writer made several inoculations (tables 1 and 2) on apples of
different varieties, using different strains from bark and fruit. In all
cases pure cultures of the fungus were used. In making wounds to serve
as infection courts a flamed scalpel was employed. Material transferred
from the culture consisted of mycelium and spores; this was inserted
in the injury previously made, and the fruits were placed in sterile moist
chambers. It is to be noted from table 1 that different strains vary in
their ability to infect the same variety. Attention is called to a comparison
of strains 1, 2, 3, and 4. All were used on Baldwin apples on the same
date and under similar conditions, yet the results were different. Strains
1 and 3 showed slow decay, with no pycnidia after nineteen days. On the
other hand, strains 2 and 4 caused rapid decay and abundant pycnidia
in the same length of time.

As shown in table 1, nine different varieties were inoculated with the
same culture, the results being variable with reference to decay, fruit
body production, and the formation of concentric rings.

It has been commonly observed that older cultures produce the disease
less readily than do younger cultures. The best results were obtained
by the use of cultures not more than two months old.

LEAF SPOT OF APPLE. Various theories have been advanced to explain
the cause of the leaf spot disease. In 1902 Stewart and Eustace (1902: 228)
believed spray injury to be the responsible agency. They further suggest
(page 232 of same reference) that drops of rain act as lenses and so con-
centrate the rays of the sun, overheating the tissues beneath. The belief
is ultimately expressed by them that the large proportion of leaf spot
in New York is due to spray injury and is not of fungous origin. Frost
has been considered the causal factor by Stone and Smith (1903) in

BULLETIN 379

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81

Biack Rot, LEAF Spot, AND CANKER OF PomackEous’FRuits

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BULLETIN 379

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Brack Rot, Lear Spot, AND CANKER OF PomaceEous Fruits 83

Massachusetts. They write: ‘No organism was to be found as the cause
of the injury, and from the sequence of events there could be no reasonable
doubt that the frost was the destructive agency.”

The fungus theory was probably first favored by Alwood (1892:59),
who attributed brown spot to Phyllosticta pirina. This organism has
been regarded as the causal agent by several other writers — Kinney
(1895 b), Lamson (1899), and others. In 1895 Stewart (1896) found a
new species of Phyllosticta, described as Phyllosticta limitata, responsible
for an epiphytotic of leaf spot on Long Island. In to907 the fungus
Phyllosticta pirina Sacc. was transferred to the genus Coniothyrium by
Sheldon (1907), and the organism is now designated as Contothyrium
pirina (Sacc.) Sheldon. Another species of Phyllosticta, P. prunicola
Sacc., is listed by Tubeuf and Smith’ as the cause of spotting of leaves of
apple, plum, cherry, and apricot.

Alwood (1898 a) records, in addition to P. pirina, other fungi associated
with the leaf spot, including Hendersonia Mali and Sphaeropsis Malorum.
This is the earliest record that the writer has seen of the occurrence of
the last-named fungus on leaves of apple, although Clinton (1902, and
1904:298) reports it as the common cause of leaf spot in Illinois and
Connecticut in later years. The question of its relationship to the leaf
spot disease, as well as that of other fungi, was subsequently - studied
by various pathologists.

Scott and Quaintance (1907) state that several different fungi, most
prominent among which are Phyllosticta sp., Hendersonia sp., and
Sphaeropsis Malorum, are connected with spots and may be responsible
for the injury in some cases, yet they are not clear as to which are the
real parasites. The following year the subject was investigated by Hartley,
I. M. Lewis, and Scott and Rorer. Hartley (1908 b), in examining leaf
spots of apple from the West Virginia Agricultural Experiment Station,
found the following fungi: Coryneum folticolum, Coniothyrium pirina, an
undetermined species of the Tuberculariae, Sphaeropsis Malorum, Mono-
chaetia Mali, Pestalozzia breviseta, Phyllosticta limitata, Torula (?) sp.,
Macrosporium sp., Ascochyta sp., Phyllosticta (?) piriseda (?), Phoma Mali,
Septoria piricola (?), Metasphaeria sp., and an undetermined species of
Leptostromaceae. He expresses the opinion that probably Coryneum
foliicolum was formerly reported as a Hendersonia. The fact that the
parasitism of Coniothyrium pirina was questioned by Stewart and Eustace
(1902:228) led Hartley to investigate the pathogenicity of this species.
He found that it would not affect healthy tissue, but that on the other
hand, when wounds such as scalding, abrasion of epidermis, or punctures

7 Tubeuf, K. F. von, and Smith, W. G. Diseases of plants induced by cryptogamic parasites, page 463.
1897-

84 BULLETIN 379

with hot and cold needles, were made in the tissue, the fungus in most
cases grew and fruited. He concludes that C. pirina is a facultative, or
wound, parasite only, and further that its ability to cause leaf spot in
orchard trees to any extent remains to be demonstrated. In his opinion
Coryneum foliicolum is less parasitic in the field than Coniothyrimm
pirina.

I. M. Lewis (1908: 367) writes as follows regarding the leaf spot situation
in New Hampshire: “‘ Believing that the exact relation of all the fungi
associated with the spots had not been thoroughly tested, an investiga-
tion was begun during the past summer to determine, if possible, the
cause of the disease as it occurs in this State, and means of control by
various spray mixtures.’’ He states further (page 368 of same reference)
that on isolation it was found that the fungi predominating were Comio-
thyrium pirina, Coryneum foliicolum, Sphaeropsis Malorum, Alternaria sp.,
and one of the Tuberculariae. To Hartley’s total list of fungi associated
with apple leaf spots, C. E. Lewis (1912: 51) adds Cladosporium herbarum
(Pers.) Link and Dematium pullulans De Bary, while Brooks and DeMeritt
(1912:182) report the isolation of a Fusarium. The first series of experi-
ments made by I. M. Lewis (1908), on August 1 showed that many inocula-
tions did not result in infections; from this Lewis reasons that “the
period at which the leafis naturally infected is earlier in the spring and
summer.’’ This view is upheld by C. E. Lewis (1t912:55), who concludes
that the older leaves are not so susceptible to infection as are young
leaves; the work of Brooks and DeMeritt (1912: 190), however, in which
they conclude that infection may occur until the last of August, indicates
that the question of biologic races was a factor overlooked by both
I. M. Lewis and C. E. Lewis. As regards the general conclusions of
I. M. Lewis’s work it may be further quoted (1908):

As a result of this season’s inoculation experiments it is impossible to offer more than
negative results as to the cause of the spots. I am of the opinion, however, that the
fungus Sphaeropsis malorum which is known to cause canker of apple limbs and is an
active parasite, will be found to be the primary cause of apple leaf spot. This sup-
position must, however, be supported by direct experiment before it can be definitely
affirmed for the spots considered in this investigation.

The same year the results of further investigations by Scott and Rorer
(1908) were published, in which a definite conclusion was reached. They
state (page 49 of reference cited): ‘‘ It was found that Sphaeropsis mal-
orum, contrary to the general belief, is the cause of the disease.’ Regard-
ing the associated species they conclude (page 52 of same reference):

Coniothyrium pirina (Sacc.) Sheldon, although it occurs abundantly on apple leaf-
spots, appears to have nothing to do with their formation.

The several other fungi that were tested, such as Hendersonia sp., Coryneum sp.,
Pestalozzia sp., and Alternaria sp., proved to be non-parasitic in these experiments and
probably occur on leaf spots only as saprophytes.

Brack Rot, Lear Spot, AND CANKER OF PomacEous Fruits 85

The work of Scott and Rorer is practically confirmed by C. E. Lewis
(1909). After making several inoculation experiments the latter writes
(1912:55), in agreement with Hartley (1908 b), as follows:

The results of these inoculation experiments seem to indicate that Sphaeropsis is
able to attack the leaves of orchard trees when they are inoculated early in the season
under favorable conditions for growth. No spotting has been produced by any of the
other fungi which have been tested although it has been found that they grow readily
on dead spots which have been killed by other causes.

The investigations of I. M. Lewis began in 1908 and were continued by
Brooks and DeMeritt in t909. As Brooks and DeMeritt state (1912:183),
the summer’s work was not conclusive. Later cultural work revealed to
them great variation in the nature of growth of different strains of the
fungus, and also in the time required for spore production. It has been
mentioned elsewhere (page 68) that these authors found morphological
strains. This discovery led them to investigate.the correlation between
the morphological and biological variations of these forms. Their final con-
clusion (page roo of reference cited) is: “Several strains of Sphaeropsis
Malorum may be obtained, varying in general vigor and in power to produce
diseased conditions. The large-spored form, with single-loculed, ostiolate
pycnidia is largely responsible for the production of leaf spot.’’

The writer performed inoculation experiments in an attempt to produce
apple leaf spot during the summers of t9r10 to 1913 inclusive. In the
experiments of 1910 the leaves of mature trees were inoculated in the follow-
ing manner: Pycnidia were removed from pure culture and the spores
liberated by crushing the fruiting bodies in a watch glass containing water.
The contents of the watch glass were removed to an atomizer and the
spores were sprayed on both surfaces of the leaves. In some cases the
leaves were previously wounded with a needle, in others they were left
uninjured. Data regarding the source of the fungus, the variety and age
of the tree whose leaves were inoculated, the date of inoculation, the number
of leaves inoculated, and the results, for 1910 to 1913, are given in table 3.
It is to be noted that no moist chamber was provided in any of the
experiments of rgro. — In 1orr a series of inoculations made on May 27
resulted in infection where wounds and moisture were provided. The
method of work here was the same as in 1910, except for the provision of
a moist chamber. This consisted of a lamp chimney, into which the in-
oculated leaves were inserted and the ends of which were closed with
damp cotton. The series of inoculations performed in July, 1910, and in
August, 1911, should be compared. In neither case was a moist chamber
used and the results were negative. In the experiments of 1912 and 1913
no spotting of the foliage was obtained by artificial inoculations. The
writer has no explanation to offer. The explanation offered by Brooks

BULLETIN 379

86

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Brack Rot, Lear Spot, AND CANKER OF PoMACEOUS’FRUITS 87

and DeMeritt (1912) for the leaf spot problem in New Hampshire is
apparently not applicable under western New York conditions, since a
variety of morphological forms was used in the inoculation work. The
results obtained indicate that there is no correlation between morpho-
logical and biological characters with respect to pathogenicity.

CANKER OF APPLE. Waite (1808 a) was the first to attribute the canker
to a fungous parasite; he suggested that Schtzophyllum commune Fr. was
the causal organism. Paddock (1899 b:183) found dark spores on the
cankers, but supposed they belonged to some saprophytic form. How-
ever, he grew this organism, as well as Schizophyllum commune, on artificial
media, and made pure culture inoculations in the following manner: A
small opening was made in the bark by means of a sterilized knife, and a
small quantity of material from bean stem cultures was inserted between
the wood and the bark. The incision was covered with moist filter paper
and kept moist for thirty-six hours. All the inoculations made in 1898
with the dark-spored fungus on apple trees were successful; other fungi
failed and the wounds soon healed. Paddock’s conclusions are sum-
marized in the following words (page. 184 of same reference): ‘‘ These
experiments showed conclusively that the dark-spored fungus can pene-
trate living apple-tree bark under certain conditions and produce a
cankered condition of apple-tree limbs and also indicated that it may pro-
duce a diseased condition of pear-tree bark.’ Again he says (page 185 of
same reference): ‘‘ The result of over fifty inoculations made from cul-
tures that were obtained from cankered apple tree limbs prove that the
apple-tree canker of New York apple orchards is caused by a fungus of
the genus Sphaeropsis.’’ Over one thousand inoculations were made by
him in 1899 (pages 200-201 of same reference) and only a very few gave
negative results. He further asserts that the fungus causes canker of the
quince if the material from pure culture is inserted under the bark,
whereas under other conditions the experiments were not conclusive.

Paddock’s work was continued (1900) for the purpose of confirming
former results and to determine if possible the relationship between the
species of Sphaeropsis that occur on various plants. He obtained cultures .
from apple fruit and apple bark, and inoculated the apple tree and other
plants. The results were positive, thus further proving the pathogenicity
of the organism, as well as establishing the identity of the fungus on fruit
and bark. The conclusions reached by Paddock are essentially con-
firmed by C. E. Lewis (1909:188-189) and by McCready (1910).

The writer (1913: 293) has summarized the results of earlier inoculation
work as follows:

During the past summer [1913] several inoculations have been made with cultures
from the ascospores of the ascomycetous fungus. The apple, pear, quince, crab apple,
and other plants were inoculated, in each case wounds being made to serve as infection

88 BULLETIN 379

courts. Three varieties of apples, namely Twenty Ounce, Baldwin, and Chenango
Strawberry, were inoculated between May 20 and July 16, 1913. Eleven sets of experi-
ments involving about seventy incisions were made, all of which gave positive infections,
the checks remaining healthy.

The above quotation concerns the ascomycetous fungus from apple.
A morphologically similar organism on Hamamelis virginiana did not
produce infection, as is seen from the following statement (Hesler,
1913:293): ‘‘About twenty-five different inoculations were made [with
the ascomycete from H. virginiana] on all the plants mentioned above
but no infections occurred.”

The writer has carried on inoculation experiments during the past
four years, both in the greenhouse and in the field, the most of the work
being directed toward the infection of bark tissues. The methods employed
have already been described (page 79). The results discussed at this
point concern only experiments in which apple strains of the fungus
(Physalospora Cydoniae Arnaud [= Sphaeropsis Malorum Berk.]) were
used on apple itself. The more important points in this regard are shown
in table 4, indicating the source of the strain, the variety and age of the
tree inoculated, the conditions under which inoculations were made, the
number of inoculations, and the general results. The infection work done
in the summers of 1910, 1911, and 1912 was not conclusive, but with
the use of various strains more satisfactory results were obtained in the
season of 1913.

It may be noted in table 4 that races of the fungus came from different
varieties of apple, isolations being made from fruit, leaf, and bark. It was
desired to determine if possible whether strains obviously living under
saprophytic conditions, as those following winter injury and fire blight,
were capable of inducing bark injury, and to determine the nature
of the parasitism of certain other strains that appeared to be parasitic.
The results on these points are conflicting and it seems that the strains
are as variable in their biological relationships as in their morphological
characters. A race may produce infection on slightly wounded bark
after it has been living under saprophytic conditions, for example, following
‘fire blight. Again, those strains which in nature appear to be acting
parasitically may prove to be weak parasites, producing infection only
under certain conditions. :

Conflicting results along this line have raised the question of individual
variation among varieties of the host plant as regards susceptibility or
immunity. It is possible that individual hosts in the same or in different
orchards may differ in this respect, but conclusive data are not at hand
with which to answer the question.

The variable results of inoculations of the apple with the apple fungus
indicate that the production of infection requires the proper strain, a

89

Brack Rot, Lear Spot, AND CANKER OF PomMACcEousS FRUITS

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Brack Rot, Lear Spot, AND CANKER OF PoMACEOUS FRUITS 93

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Brack Rot, LEAF Spot, AND CANKER OF PoMACEOUS FRUITS 95

wound in which to initiate the relationship, and moisture until infection
has occurred.

Associated species— It has been noted elsewhere that the fungus
Schizophyllum commune Fr. was suspected as being the cause of canker
(Waite, 1898a). This apprehension was undoubtedly based on asso-
ciation of the fruiting body of the organism with the lesions, as it is common
to find this fungus fruiting on old cankered limbs. Paddock (1898 a)
cultured this species and after inoculating apple limbs concluded that
it was not the cause of the disease.

The rdéle of associated species in the production of canker on apple
is taken up somewhat at length by C. E. Lewis (1912). In Maine the
fungi most frequently found on dying twigs and branches of apple are
Sphaeropsis Malorum, Myxosporium corticolum Edgerton, Coryneum
foliacolum Fckl., Cytospora sp., Phoma Mali Schulz & Sacc., and Conio-
thyrium pirina (Sace.) Sheldon. Those often developing in plate cultures
were: Phyllosticta limitata Peck, Dematium pullulans De Bary, Clado-
sporium herbarum (Pers.) Link, Alternaria sp., Macrosporium sp., Fusarium
sp., Epicoccum sp., and Glomerella cingulata (Stonem.) Sp. & von Sch.
To this list the writer adds Septoria sp., Cephalothecitum roseum Cda., and
Aspergillus sp. C. E. Lewis (1912:62) concludes “that Coryneum and
Phoma can cause considerable injury to young trees and branches of
orchard trees. Myxosporium and Cytospora do not attack healthy
branches but it seems probable that they attack weakened branches.”’
The writer’s results with the various associated fungi may be summarized
by the statement that none of the species enumerated above made growth
on apple bark.

CROSS-INOCULATIONS AND HOST RELATIONSHIPS (Plates vill, IX, XI, XIV).
The identity of the various species of Sphaeropsis on the same and on
different plants has been established in certain cases. That the species on
the fruit of apple is the same as that on the bark was proved by Pad-
dock (1899 b, 1900) several years ago, and confirmed by Potebnia (1907)
more recently. A similar relationship for the fruit and foliage forms
of the fungus has been proved by Morse (1909), while Scott and Rorer
(1908) have demonstrated the identity of the organism on leaves and
bark. The ability of these three forms to grow interchangeably on the
several organs of the apple is no longer questioned, and the results of
previous investigations are essentially confirmed by the writer in tables
iy 2aese and. 4.

The pycenidial stage of Physalospora Cydoniae Arnaud (Sphaeropsis
Malorum Berk.) has been collected by various investigators (Paddock,
Arnaud, the writer, and others) on the following plants: apple (Pyrus
malus L.), apricot (Prunus armeniaca L.), alder (Alnus glutinosa Gaertn.),

BULLETIN 379

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98 BULLETIN 379

ash (Fraxinus americana L.), basswood (Tilia americana L.), bittersweet
(Celastrus scandens L.), box elder (Acer negundo L.), cherry (Prunus
avium L., P. pennsylvanica L., P. virginiana L.), cherry laurel (Prunus
lauro-cerasus L.), crab (Pyrus coronaria L.), currant (Ribes sp.), dogwood
(Cornus stolonifera Michx., C. sanguinea L.), elder (Sambucus cana-
densis L.), elm (Ulmus americana L.), fig (Ficus carica L.), grape (Vitis sp.),
hawthorn (Crataegus oxyacantha L.), hop hornbeam (Osirya virginica
[Mill.] K. Koch), lilac (Syringa vulgaris L.), maple (Acer saccharinum L.),
mulberry (Morus alba L.), oak (Quercus alba L., Q. prinus L.), osage
orange (Maclura pomifera [Raf.] Schneider), peach (Prunus persica
[L.] Stokes), pear (Pyrus communis L.), persimmon (Diospyros
virginiana L.), pine (Pinus strobus L.), plum (Prunus domestica L., P.
triflora Roxbg.), quince (Cydonia vulgaris Pers.), rose (Rosa canina L.,
Rosa sp.), rose of sharon (Hibiscus syriacus L.), spicebush (Benzoin
aestivale [L.] Nees), sumac (Rhus typhina L., R. glabra L.), sycamore
(Platanus orientalis L.), witch-hazel (Hamamelis virginiana L.). Where
fresh material was available the writer cultured the fungus from all these
plants except three — dogwood, lilac, and rose of sharon, which have just
been collected — and these cultures were used in all cross-inoculation
experiments. The source of the cultures used, the plants inoculated, and
the results, are shown in table 5. The methods used were similar to
those described in connection with the inoculation experiments on apple
fruit (page 79). In some of the earlier experiments a moist chamber
was used consisting of a petri-dish lid, the inner margin of which was lined
with damp cotton. Later the glass lid was eliminated and a cotton cap,
made by rolling a strip of cotton about the finger, wasemployed. Moisture
was provided at the time of inoculation and was added daily for several
(usually from three to seven) days subsequently.

The results of cross-inoculations were not conclusive, particularly in
cases in which the fungus failed to develop. Failure to produce infection
may be accounted for in two ways: either the fungus was not parasitic
on the plant inoculated, or conditions favorable for infection were lacking.
In many cases further trials are desirable.

In nature the fungus rarely shows a parasitic tendency on wild plants —
with the exception of Quercus prinus (see Rankin, 1914) — but it is
generally found developing on dead and fallen twigs; cankers have not
been observed which could with certainty be attributed to this organism.
On cultivated plants it commonly shows the same habits as it does on wild
plants, or it may develop in healthy tissues, resulting in the formation
of a canker. Here, then, on’ the cultivated plants are found both sapro-
phytic and parasitic tendencies. This phenomenon is in accordance with
the commonly accepted theory that parasitism originated from sapro-

: Brack Rot, Lear Spot, AND CANKER OF PoMAcEOUS FRUITS 99

phytism. This is what is to be expected; and the theory is further sup-
ported by inoculation data which show that the strains from wild plants
may be induced to infect cultivated plants. The reverse process — that
is, the infection of wild plants with strains from either cultivated or wild
forms — has been almost wholly unsuccessful in the writer’s experience.
This in the main confirms the work of Paddock (1899 b, 1900).

On certain wild plants there is found a saprophytic race which, when
carried to cultivated forms such as the apple or the pear, acts as a wound
parasite. On cultivated plants the fungus follows fire blight and winter
injury, and hence is a saprophyte, but the latter strains are not necessarily
obligate saprophytes since they have been induced to cause canker by
artificial inoculation. This is shown by strains 22, 38, 57, and 7o in table 4.
It does not appear, therefore, that the fungus can be segregated easily
into physiological groups, since varying degrees of parasitism are exhibited
by a given race.

From the experiments described and tabulated it is clear that there is
considerable variation in the virulence of races, but just how long a given
parasitic strain will retain this mode of life is a difficult question to answer.
The ability of the organism to act as a wound parasite, and to adapt itself
naturally to the saprophytic mode, makes it a serious pest from the stand-
point of control. Its ability to remain saprophytic indefinitely until the
host is injured in some way only increases the difficulty in alleviating the
disease.

NAMES AND SYNONYMY

The work that has been done on cross-inoculations and on the mor-
phology of Sphaeropsis from several different plants makes it apparent
that there is one large polymorphic species. It is true that many inocula-
tions failed, and that two given races may differ widely in their mor-
phology; but there is considerable evidence that these characters are
variable and are not important in taxonomic considerations.

The several forms as they have been described from time to time have
been given a specific name, usually one for every host plant. This pro-
cedure has resulted in the accumulation of a large number of specific
names which could now be disposed of only by the examination of type
material of each so-called species. Several generic names have become
involved in the synonymy of the fungus, due to the indefinite limitations
and wide variations, and consequent overlapping, of certain form-genera.
Saccardo (1884 a) believed Sphaeropsis Malorum Berk. to be a Phoma,
_since it was originally described by Berkeley (1836) as having yellowish
green spores. It is now known that the young spores have this color
characteristically, and furthermore Dr. C. L. Shear, who has seen Berkeley’s

100 BULLETIN 379

type, has stated (in conversation with Dr. Donald Reddick, of Cornell
University) that the organism is unquestionably identical with Sphaerop-
sts Malorum as now recognized. Subsequent to Saccardo’s use of the name
Phoma, this genus was divided into Phoma and Macrophoma — the former
genus containing species with spores less than 15 long, the latter con-
taining species with spores more than 154 long. Thus Phoma Malorum
(Berk.) Sace. was renamed by Berlese and Voglino (1886) as Macrophoma
Malorum (Berk.) Berl. & Vogl.

It appears that certain species of Sphaeropsis have been confused with
those of Diplodia. The two genera are separated on the basis of one-
celled spores in the former and two-celled spores in the latter. But
both genera fail in their chief distinction, so that mycologists have been
misled on this point. Ftckel (1869:393) used the name Diplodia pseudo-
diplodia Fckl. in describing the fungus on branches of apple; elsewhere
(page 395 of same reference) he used Diplodia Malorum Fckl.

It has been noted previously that the pycnidium sometimes approaches
and even reaches the condition characteristic of the form-genus Botryo-
diplodia. It becomes evident that the names of certain species of this
genus may stand oniy as synonyms of Physalospora Cydoniae Arnaud.

The origin of several of these synonyms has been discussed in an earlier
paper by the writer (1912), to which the reader is referred. At that time
it seemed desirable to attempt the selection of the name that should,
according to the rules of priority, be applied to the pycnidial stage.
Recently, however, the perfect stage of the fungus has been found, and thus
the selection of a specific name from the pycnidial forms is of minor
importance. The generic name now becomes Physalospora, and the
writer has chosen Cydomiae as the specific name. The following state-
ments bearing on this question are quoted from another paper by the writer
(1913:295):

The problem of selecting a specific name is somewhat perplexing. The organism
with which the writer is dealing strongly resembles P. Cydoniae Arnaud but we have
not seen his type material and there remains the question of whether his fungus has not
been previously described. In this connection a few species which suggest this possi-
bility may be noted: P. entaxia E. & E., P. festucae (Lib.) Sacc. and P. nigropunctata
Romell, the last on limbs of Pyrus malus according to Saccardo. Until further data
are at hand the writer is inclined to accept tentatively the name Physalospora Cydoniae
Arnaud.

Soon after the above-mentioned paper appeared in print, the writer
received from Arnaud a glycerin-jelly mount of his type material. It
is clear that morphologically the organism is identical with the one
described by the writer (1913) under the same name. But the question
of the specific name is still unsettled, for it is not improbable, as stated
above, that the organism has been previously described under some other

specific name. This problem, as in the case of the several pycnidial

Brack Rot, Lear Spot, AND CANKER OF PoMacEOoUS FRUITS tor

forms, wouid involve the study of type material, which as yet has not
been available to the writer. Under the circumstances Arnaud’s specific
name will be retained tentatively by the writer. The following is a
partial list of species which are concerned in the synonymy of the fungus;
citations to literature are also given:

Physalospora Cydoniae Arnaud. Ecole Nat. d’Agr. Montpellier.
MMataly WAI. “aioe

Sphaeria sumacht Schw. Amer. Phil. Soc. Trans. n. s. 4:205. 1834.
Sphaeria rhuina Schw. Amer. Phil. Soc. Trans. n. s. 4:218. 1834.
Sphaeria pomorum Schw. Amer. Phil. Soc. Trans. n. s. 4:219.. 1834.
Sphaeria Malorum Berk. English Flora 5:257-258. 1836.

Diplodia pseudodiplodia Fckl. Symbolae Mycologicae, p. 393. 1869.
Diplodia Malorum Fckl. Symbolae Mycologicae, p. 395. 1869.
Sphaeropsis Cydoniae C. & E. Grevillea 6:84. 1878.

Sphaeropsis Malorum Peck. Sylloge Fungorum 3:294. 1884.

Several years ago Ellis (1880) studied the variability of Botryosphaeria
fuliginosa (M. & N.) E. & E. [- Sphaeria Quercuum Schw.], and came to
the conclusion that this species really included at least eighteen so-called
species. Among these may be noted, using Ellis’s nomenclature, Sphaeria
entaxia C. & E. [= Physalospora entaxia Sacc.], S. viscosa C. & E. [= P.
viscosa Sacc.], S. erratica C. & E. [= P. erratica Sacc.], Botryosphaeria
pustulata Sacec., and others. Ellis found wide variation with respect to
stromatic formation. Sometimes the perithecia were scattered and
distinct, and again they were confluent and united in a stroma. Consider-
able range with respect to the ostiolum is also noted by Ellis (1880). But,
as stated by Ellis and Everhart (1892:547), certain forms of Botryo-
sphaeria fuliginosa—those lacking a stroma—are removed to the genus
Physalospora. It may be that under certain conditions P. Cydoniae
develops a stroma, but such a tendency has not been observed; for this
reason the generic name Physalospora is selected.

LIFE HISTORY STUDIES

The mature morphological structures of the fungus have been described,
so that the following paragraphs concern only the successive stages in its
development: where and in what condition the organism hibernates, the
manner in which it is disseminated, its entrance and effects on the plants
attacked, and the development of certain of its fruiting bodies.

SOURCE OF THE INOCULUM. ‘The fungus passes the winter as mycelium
in the tissues of the host and as pycnospores in pycnidia. If a canker
is examined in the spring when growth is resumed by the host plant,
the margin of the old lesion may show discoloration. The writer has
frequently planted bits of the bark from the edge of a canker in agar
plates, pure cultures resulting. This is evidence of the resumption of
growth of the mycelium in the old lesion. It is stated by Caesar (1909)

To2 BULLETIN 379

that as a rule the fungus does not die out but continues to extend in every
direction year after year, finally girdling the limb. In this connection
Paddock (1899 b:189) writes as follows: “In some instances the
mycelium apparently lives over winter and continues its growth the
following spring. The formation of the largest cankers can scarcely
be explained in any other way.”’ He adds, however, that “‘in all of the
inoculations made in the spring of 1898, in only one instance did the
resulting canker enlarge any during the present season.”

The writer’s experience in this regard is somewhat similar, although
more cankers have enlarged the second year than is intimated Fy Paddock.
On this point there appears to be a difference in orchards. In one orchard
the author counted forty cankers on three trees on May 20, 1912. All
were formed at least one year previously, but only one showed advance-
ment at the margin on this date. In other orchards a majority of the
cankers were enlarging. The vitality of the trees does not seem to
explain the difference displayed, since this quality appeared similar in the
two cases mentioned. The trees in the two orchards were of the same
variety (Twenty Ounce); here the question of physiological races may
throw light on the subject.

It has been suggested that the mycelium may winter over in mummified
fruit, and that in cases in which the fruit hangs on the tree the hyphz
may pass into the branch supporting it (Anonymous reference, 1899 ¢,
page 126). The latter condition has not been observed by the writer.
In some cases the mycelium hibernates in the mummified fruit, but the
passage of the hyphze down into the branch and the resulting development
of a canker is questionable.

The growth of the mycelium at the edge of a lesion, as described ators
does not account for new and isolated cankers. The phenomenon results
nevertheless, indirectly, in a source of inoculum, in that fruit bodies may
develop on the newly infected margin and so furnish spores which may
cause other infections directly. The young cankers originate by the
agency of the spores of the fungus.

It is a common thing to find, in the winter and spring, pycnidia bearing
mature spores on mummified fruits. These fruiting bodies may be
observed also on cankers and on fallen twigs, bark, and leaves. In western
New York cankers and dead twigs are the most important sources of
the inoculum.

The hibernation of pycnospores on the various organs of the tree is
reported by a number of investigators: on the bark, fallen twigs, and
cankers, by Paddock (1899 b: 189), by Brooks and DeMeritt (1912:189),
and by Scott and Roret (1908: 52); on fallen leaves by Reed and Cooley
(z911); on the fruit, as mummies hanging on the tree or fallen, by Scott

Brack Ror, Lear Spot, AND CANKER OF Pomacgous FRuITS 103

and Rorer (1908:52) and by Brooks (1909). Other writers have con-
firmed all these observations. These spores in winter have been placed
in room temperature, and were subsequently found to be capable of
germination in tap water. There is evidence that pycnospores may
also winter over scattered about on the bark; they have been found in
early spring before the pycnidia have entered their period of spore discharge.

The réle of the ascosporic stage in hibernation is not certain. As
previously indicated, the perithecia are rare on Pyrus malus in New
York, and it would seem, therefore, that the ascospores from this source
are of relatively little importance in initiating infections. Whether
this stage is common on other plants in this State, and important as
a source of inoculum, are matters remaining to be investigated.

METHOD OF SPORE DISCHARGE. ‘The manner in which the pycnospores
escape from the pycnidium has not been fully described, so far as the
writer knows. Berkeley (1836) makes mention of the process as follows:
“When dry the ostiolum is frequently crowned with a short minute ten-
dril oozing out from the perithecitum.’’ Halsted (1892) writes: ‘‘ The
ripe spores . . .- . _ form long, slender coils as they are pushed
out of the small hole in the skin.” Similar descriptions of the process
are given by Clinton (1902) and by Evans (1910).

If a bit of bark or of fruit bearing pycnidia is placed under moist con-
ditions, in a few hours dark masses of spores in the form of a coil may be
seen (Plate xm, 4). In one experiment the following notes were taken:
“Twigs of an apple strain (no. 82) bearing mature brown pycnospores
were placed in a moist chamber on May 20, 1913, at 3 p. m. By noon
on May 23 the dark masses could be seen with the naked eye. These
masses measure about 200 to 2504 by 4oo to 450y.’”’ At this time it
was observed that the masses stood out from the surface of the bark
nearly five millimeters. They were very easily removed by a needle
and examined under the microscope. It was observed that on the side
of the mass nearest the bark several spores had germinated, and the
resulting hyphe had raised the mass away from the surface of the bark.
A drop of water was added to one mass, which behaved as follows: In
a few seconds the mass began to segregate, and single spores or groups
of a few moved very quickly, with a darting motion, from the mass. They
were at first thrown through the drop of water as far as 85 4 and they
then moved slowly away. After forty-five minutes the spores had scattered
in all directions, from 1500 to 2800 from the original point of departure.
The coil in some cases contained about 1500 mature spores and in some
experiments proved to be at least one millimeter in length. It has been
estimated by the writer that there may be as many as 150 pycnidia on
a square centimeter of the surface of an apple fruit; this would furnish

104 BULLETIN 379

approximately 225,000 spores for the given unit area, or 1,406,250 spores
per square inch of apple surface.

As stated in the notes quoted above, the spore coils were found on the
bark three days after moisture was supplied. But this does not mean that
all this time was involved in the process of escape. The pycnidia were
found to be closed at first and considerable time must have been con-
sumed in their opening. In other experiments as long a period as five
days was necessary to effect the opening in some cases. The time that
actually intervenes between admission of moisture to the spore mass
within the pycnidium and the coiling of the spores is negligible. Pycnidia
have been removed from dry bark in the summer, placed on dry slides,
and observed with the microscope. If a drop of water is then applied,
the spores will ooze out immediately provided the ostiole is open. Their
fate after coiling seems to depend on the amount of moisture present.
If a beating rain is falling, undoubtedly the spores are carried by the
spattering drops toward the ground and perchance lodge on the foliage
or on the branches. In case of a dew, unquestionably the coil behaves
as described above; that is, some of the spores on the lower side of the
mass germinate, the resulting weft of germ tubes raising the spores from
the bark, when they may be lifted by the wind. Again, if the mass
encounters a drop of water the gelatinous material quickly expands and the
spores are scattered throughout the drop. It is conceivable that the
drop may be carried by the wind for a short distance at least.

TIME OF SPORE DISCHARGE. ‘The time of the year when spores are dis-
seminated may be approximated by noting the date of the first appearance
of the diseased spots, and by keeping careful watch of the behavior of the
pycnidia in the field. It is believed by I. M. Lewis (1908) that the period
when foliage is naturally infected is early in the spring and summer. The
same opinion is expressed by Brooks (1909), who states that the indi-
cations are that leaf infection ceases in June. Later, however, Brooks
and DeMeritt (1912:189) attach little value to this statement, expressing
the opinion that the nature of the fungus was a factor overlooked by
previous investigators and that weather conditions may play a part in
determination of the time of infection.

Paddock (1899 b: 189) states that many spores remain in pycnidia until
the following spring, when they are disseminated. Wolf (1910) has made
a study of the prevalence of fungus spores in orchards by exposing agar
plates, and his conclusions are expressed as follows (page 202 of reference
cited): ‘‘At no time during the period in which exposures were made
(September to May, inclusive) were viable spores of Sphaeropsis malorum
present in the atmosphere of the orchard.” McCready (1910) reports
mature spores as being disseminated from cankers as early as the first

Brack Rot, LEAF Spot, AND CANKER OF PoMACEOUS FRUITS 105

week in April, and states that at the same time a large number of spores
were found in the orchard on rotten apples. In Virginia, at Blacksburg,
Reed and Cooley (1911) found spores being discharged from pycnidia on
leaves on June 25, 1910. Whether spores are liberated at an earlier date
these authors do not state, but it is probable that such is the case.

From observations made by the writer it seems that the date of first
discharge in the spring varies with the season. Apparently the ostiole
does not open at a temperature below 60° F. (15.5° C.) or in the absence
of moisture, and a period of humidity of several hours duration is neces-
sary. The dates for spore discharge observed at Byron, New York,
are May 16, 1912, and May 12 and 23, 1913. In 1911 spores were found
coiling on July 17, but the process must have occurred earlier. That
they continue to be liberated throughout the summer is shown by the
appearance of new infections on foliage from May until September 20,
1913. In 1911 several young spots were found on bark in the middle of
August. Ripe and green fruit infections also show that spores are dis-
seminated in August and September.

AGENTS OF DISSEMINATION. It is clear that the behavior of the
pycnospores on being discharged places them at the disposal of wind, rain,
and possibly insects, depending largely on the conditions of moisture.
Halsted (1892) states that “the germs pass . . . . through the air
or by means of the various insects that visit the fruits, especially those with
broken surfaces due to partial decay.”’ A similar opinion is expressed by
Sturgis (1894). Lamson (1902:76) states that the spores are easily floated
in slight currents of air, while Bethune (1909:29) and McCready (1910)
attribute dissemination to the wind.

The writer has observed numerous cases of the disease in isolated situa-
tions. In some orchards there was abundant leaf spot but no cankers
were on the trees. Here the wind probably acted as the agent, carrying
the spores from plants outside the orchard. That the rain washes the
spores to the foliage is shown by the cone-shaped area of infections beneath
cankers and diseased fruits.

Insects are no doubt agents in the dissemination of the organism. The
gelatinous nature of the spores renders them sticky and they may adhere
to the feet of insects. In June, 1913, the writer found spores on the feet
of the rosy apple aphis (Aphis sorbi Kaltenbach), but it is his opinion
that insects are of little importance in carrying the spores. Their réle
in making openings in the fruit and bark is probably much more important.

INFECTION couRTs. The fungus shows little preference for any par-
ticular type of injury as a means of entrance. It is not able to penetrate
healthy tissue of the bark and fruit, but follows other fungi such as
Glomerella cingulata (Stonem.) S. and vS. on fruit, as noted by Alwood

106 BULLETIN 379

(1902:257). Other points of entrance to fruit, as listed by Burrill and
Blair (1901), are insect punctures, mechanical injuries, and the blossom
end of the apple. These authors state also that the fungus seems to start
without the aid of a wound. The writer has noted many cases in which
young lesions on the apple surrounded an opening made by the codling
moth (Carpocapsa pomonella L.). Delacroix (1903 a:140) is disposed
to believe that in some cases certain insects are able to rupture the bark,
especially that of young branches. He observed an abundance of Epidi-
aspts ptricola (Del Guer.) Ck1. on infected areas, and is of the opinion that
these insects are concerned here. Gitssow (1911) states that ‘‘apples
are infected through some injury (wasps, curculio, hail, etc., etc.).”
Arnaud (1912) believes that there is some connection between the entrance
of the fungus, and a beetle.

Observations show also that various mechanical injuries commonly
serve as points of entrance for the fungus. Such injuries as limb and
hail bruises may act in this capacity. Faurot (1912) states that rot
occurs largely on fruits the skin of which was previously broken by spray
injury and growth cracks.

Whether the healthy epidermis of the fruit is penetrated, as suggested
by Burrill and Blair (r90r), is open to question. The writer has never
been able to infect unbroken tissues of the apple fruit. On the foliage,
artificial inoculations by various investigators — Scott and Rorer (1908),
Brooks and DeMeritt (1912), and others — show that the fungus can
penetrate healthy leaf tissues. The author, however, has never been
successful in producing leaf spot without first wounding the tissue. Infec-
tions in the bark apparently occur only through some sort of wound.
Such injuries may be caused by growth cracks, as noted by Caesar (1909);
by ladders and boots, in pruning and picking; by barking by the machinery,
in cultivation; by props not carefully wrapped; by hail; by openings left
by the careless removal of water sprouts; and in other ways. Of fifteen
young cankers observed by the writer on a single tree, ten had their origin
in openings left by the removal of suckers. The writer has observed
cases in which the fungus had followed the rust fungus, Gymnosporangium
Juniperivirginianae Schw., on apple twigs. Scott and Rorer (1909: 11)
suggest that it may follow Phyllosticta solitaria E. & E. on apple buds. —
The writer has frequently isolated the fungus from lesions caused by
the blotch fungus (P. solitaria) on apple fruits sent from Indiana. As
previously noted, the fungus frequently follows fire blight and winter
injury. Morse and Lewis (1910) state that in Maine orchards much of
the disease that was called canker had its origin in frost spots of 1906—
1907, and that so far as investigated the cankers of fruit trees in Maine
orchards had their origin in wounds.

Brack Rot, Lear Spot, AND CANKER OF PoMAcEOoUS FRUITS 107

PYCNOSPORE GERMINATION (Fig. 29). The pycnospores usually ger-
minate readily in tap or rain water. The time required for the process
varies considerably, depending, no doubt, on the age of the spores. If they
overwinter, the question of their longevity arises. As a rule sexual spores
are regarded as short-lived, but it is not so in the case of this fungus.
Duggar (1909:353) says: ‘‘The spores seem to retain their vitality for a
considerable period of time, having been germinated after being stored for
a year in the laboratory.” The writer has found that spores two years old
or older may germinate in tap water after twenty-four hours. Younger
spores ordinarily germinate within five or six hours, but they may pro-
duce a tube after three hours. Spores which are dark brown in color,
often septate, and having
an older appearance, re-
quire more than twelve
hours for germination.

Usually one or two
tubes emerge from a
spore at or near the end;
germinations also occur
at the side. The de-
veloping hyphz in cul-
ture occasionally form
microconidia, or second-
ary conidia, near the
growing point ofa hypha;
these have been men-
tioned by* Delacroix
eee whores FIG. 29. TYPES AND VATASIONS OF PYCNOSPORE GERMI-
that they do not develop
further. The writer has germinated them in tap water. In some cases
peculiar types of germination occur, short, stunted tubes being developed.
In other cases the process is entirely inhibited, and in certain of these
cases the laying down of a cross-wall takes place instead. In one obser-
vation notes were made as follows:

Spores one-celled when collected (May 13, 1913). Placed to germinate in tap water
and after twenty-four hours the two-celled spores had not germinated; the one-celled
spores had developed tubes about 30 long. After forty-two hours some of the two-
celled spores developed tubes about 175 in length, whereas the germ tubes of the
one-celled forms were about 500x long.

Again, spores placed to germinate, instead of producing a germ tube,
after several days developed a septum. Another peculiar behavior of the
spores is that they may fuse in pairs. Delacroix (1903 a) describes a
peculiar type of germination of young and hyaline pycnospores in a

108 BULLETIN 379

solution of 2.5 per cent of glucose and 1 per cent of peptone. No cross-
wall was developed. After the third day the wall broke and the contents
emerged, forming a bud on the surface of the spore. This spherule may
attain a diameter of from 35 to 4oy; its further development was not
followed by Delacroix. The writer has observed similar behavior of
pyenospores, except that the swollen parts finally developed a germ
tube. This took place in tap water. In some cases older spores burst
and fail to send out a germ tube.

The effect of low temperatures on pycnospore germination was noticed
in the spring of r913 in connection with infection experiments. On May
15, 1912, spores in drops of tap water on a glass slide were placed in a petri
dish, plenty of water was supplied to prevent drying out, and the culture
was placed out of doors, where the temperature ranged between 8° and
1o° C. A second culture was kept at room temperature (21° C.). No
germinations occurred outside, but the cultures kept in the laboratory at
21° C. gave normal germinations. On May 12, 1913, the minimum tem-
perature was 9° C., the maximum 15.5° C. All spores out of doors failed
to germinate at these temperatures, while those at 21° C. gave normal
germination. On May 13; 19, and 20, 1913, when the maximum tempera-
ture was 15.5° C., similar results were obtained, except that in one culture
on May 20, at 15.5° C., a very low percentage of germination was observed.
This indicates that in most cases a
temperature of 15.5° C. is unfavorable
for germination, and that below that
point germination fails. Delacroix
(1903 a:139) states that mature spores
germinate after forty-eight hours
at a temperature of about 16° C.
(60.8° F.).

ASCOSPORE GERMINATION (Fig. 30).
The ascospores germinate readily in
tap water and potatoagar. The time
required for the process is from six to
twelve hours. In some cases a septum
is developed in the ascospore during
germination.

INCUBATION PERIOD. The period of
incubation on apple bark, as stated by

Fic. 30. STAGES IN THE GERMINATION Potebnia (1907:16), is about four

peace een days. On foliage it is about five
days, according to the observations of Scott and Rorer (1908: 50-51).
Inoculations made by the writer on bark show that the time between

Brack Rot, LEAF Spot, AND CANKER OF POMACEOUS FRUITS 109

inoculation and the first sign of the disease is from two to seven days,
varying with the strains of the fungus used and the meteorological con-
ditions. The average is four days. On fruit, discoloration appears after
from twenty-four to forty-eight hours.

PATHOLOGICAL HISTOLOGY. Fruit—If a section of an apple fruit is
made perpendicular to the surface, the cuticle, epidermis, hypodermis,
cortex, and scattered vascular bundles are in evidence. The epidermis
is composed of a single layer of rectangular cells, the outer walls of
which are strongly thickened by a waxy infiltration to form the cuticle.
Immediately below the epidermal cells is the hypodermal parenchyma,
the cells of which are distinctly different from those more deeply
seated. They are compactly arranged, comparatively small, and oblong,
with the greater diameter parallel to the surface. They contain the
coloring matter of the fruit. There is a gradual transition from these
cells to the large isodiametric cells that make up the mass of the apple
tissue. The veinlets come from ten main veins and by continued
. branching the bundles become scattered, being finally lost in the
cortex.

There is a sharp line of demarcation between the healthy and the
diseased tissues (Plate x11, 2); this is especially noticeable in the hypo-
dermal parenchyma. The coloring matter is abundant in the normal cells
of the hypodermis; at the junction of the two regions the coloration is lost
very abruptly and the tissue is a distinct brown. All the affected region
is brown and the discoloration in the cortex extends beyond that in the
hypodermis. Apparently the hypodermis is attacked along the advancing
margin of the lesion from the cortex below. The mycelium of the fungus
is found in advance of any apparent change in the normal color, and is
found in the cortex first, at a point several cells in advance of the affected
hypodermal cells. The hypodermis appears to be undermined. The walls
of the cells in this region are greatly thickened; the process is apparent
within a week after infection, and when the apple becomes mummified
the lumen of the cell is nearly closed. Dandeno (1906) states that there
is a production of cellulose in the cell wall of the apple in the course of
its decomposition. Starch is also produced in the cells invaded by the
mycelium of the fungus, but with the thickening the starch grains dis-
appear. The excessive thickening is regarded by Dandeno as resulting
in the preservation of the mummy.

The mycelium is usually, if not always, intercellular. In thick, free-
hand sections strands may be found crossing the cell cavity, but cell-wall
penetration has not been observed. Frequently small threads appear
to pass into the cell of the host from the parent branch which is in the
intercellular space, but no opening in the host-cell wall has been seen.

IIo BULLETIN 370

Such hyphz are regarded as being intercellular, merely giving the appear-
ance of an intracellular habit because of the thickness of the section;
in thin, microtomed sections
the threads are found be-
tween the cells. In certain
cases the hypheze appear to
e within the cells, but one
may mistake a large intercel-
lular space for a cell lumen.
Dandeno (1906) states that
the mycelium is intercellular,
but that small threads enter
the cells and even pass
through them (Fig. 31).

Leaves— The lesion pro-
duced on the leaf is largely
necrotic. The cells are
brown, collapsed, and ob-
viously dead. The average
FIG. 31. HISTOLOGICAL CH\NGES IN THE FRUIT OF thickness of the normal

APPLE apple leaf is about 142,
. Showing appearance of healthy tissue at let and diseased whereas that of the diseased
area is about 61 uw (Fig. 32).

The epidermal cells of the affected tissue are flattened and bear little
resemblance to normal epidermis. The palisade cells maintain their
relative position but are considerably shortened. The cells of the spongy
parenchyma are shriveled and irregular in form (Fig. 32).

In some cases the lesions are limited bya vein, and, although a small vein
may mark the extent of the
diseased area, the larger veins
more frequently act in this
capacity. In cases in which
the edge of the spot does not
fall at a vein, a plate of cells
surrounds the lesion and limits,
for a time at least, the extent
of the fungus. FIG. 32. HISTOLOGICAL CHANGES IN DISEASED

The structure of the leaf at pe

Showing healthy and diseased tissue. The beginning of

the margin of a spot is very the suberized layer, represented by heavy-walled cells in a
= ~ line from epidermis to epidermis, should be noted

different from either the
healthy or the dead parts. The process of differentiation apparently takes

place in considerable advance of the fungus. In some stained sections

Brack Rot, Lear Spot, AND CANKER OF PomacrEous Fruits rir

a row of cells with dark-stained walls is seen in the leaf (Fig. 32).
They are arranged in a direct line from the upper to the lower epi-
dermis. This involves the palisade cells and the spongy parenchyma,
the latter tissue now being composed of more densely packed, but large,
cells. With the advance of the fungus this layer increases in size and
number of cells until the diameter is increased over that of the normal
part. An additional layer of palisade cells may be developed in this
region, but in a late stage the entire mesophyll becomes densely filled
with large, irregularly shaped cells. The elongated palisade cells are
completely changed and become isodiametric in form. The apparent
stimulation results in hyperplasia and metaplasia of the palisade cells
and in hyperplasia of the spongy tissue (Fig. 33).

The diseased cells give a test for suberin with chlor-iodide of zinc and
with cyanine-glycerin. Certain stages in the development of the leaf spot
show discoloration of the epi-
dermal cells up to the suber-
ized layer only. Later, how-
ever, the epidermal cells are
affected beyond this region,
as evidenced by their loss of
normal size and color. It ap-
pears that penetration of the
temporary layer is accom-
plished by the fungusinvading py, 33- HISTOLOGICAL CHANGES IN DISEASED
the epidermal cells and thence | LEAF TISSUE
advancing into the healthy «need “Metasiesa and hyperplasia are enhibited in the
tissue. At any rate the my- ™SP?¥”
celium is found in the epidermal cells in this region. The alternate pro-
cesses of the formation of this layer of tissue, and the subsequent invasion
of the tissue beyond the suberized layer by the parasite, give rise to the
concentric rings previously described.

Bark.— The tissues of the normal apple stem represent the condition
found in a typical dicotyledonous plant. In the center is the pith,
radiating from which region are alternate medullary rays and fibrovascular
bundles. Outside these is a cylinder of secondary cortex, which is in
turn surrounded by a cylinder of thick-walled cortex (probably primary
in nature) and one of cork or periderm. In older stems the epidermis
is not present. The secondary cortex is composed of several layers of
phloem, in turn made up of hard, or lignified, sclerenchyma fibers, sieve
tubes, companion cells, and phloem parencyhma. Ina longitudinal sec-
tion the medullary rays are prominent and are perpendicular to the
periderm. In the secondary cortex these rays are connected by rows of

II2 BULLETIN 379

phloem parenchyma which are oriented at right angles to the direction
of the medullary rays. These phloem parenchyma cells are rectangular
and similar to the medullary ray cells; the arrangement of the former
results in the noticeable stratification of the secondary cortex.

The material for comparative study of healthy and diseased tissues
was usually taken so that both areas would appear in the same section.
Cankers from natural and artificial infection were fixed in Gilson’s fixer

Fic. 34. HISTOLOGICAL CHANGES IN DISEASED WOOD

Two apple twigs, showing cankers as they appear on surface. The specimens
on the right are the same twigs, with bark removed to show the streak

or in chrom-acetic acid, hardened in the usual manner, and finally imbedded
in either celloidin or collodion. Sections made from such material, as
well as from fresh tissue, were cut with a desk microtome and stained
with the following stains: safranine and methyl blue; safranine and
methyl green; phloroglucin; and a chlorophyll solution.

In the normal tissues the lignified and suberized tissues — that is,
cork and hard sclerenchyma fibers—are stained red with safranin, whereas

Brack Ror, Lear Spot, AND CANKER OF PomaAcEous FRuITS 113

the cellulose tissues, cortical and medullary, are colored blue with methyl-
blue and unstained with methyl-green. The woody parts stain red with
phloroglucin. In the diseased part there is a very prominent general
brownish deposit, located chiefly in the medullary ray cells, the thick-walled
cortical parenchyma, and the phloem parenchyma. Such cells are not
stained by any of the stains used. The sclerenchyma fibers and the cork
are colored red by saf-
ranine, whereas suberized
cork cells are made
green with a chlorophyll
solution. Diseased wood
shows a test for lignin
phloroglucin.

The more striking ex-
ternal symptoms of the
canker noted are the dis-
coloration of the bark, a
crevice at the margin of
the lesion, and a sinking
of the tissues. It has been
noted elsewhere that the
organism penetrates the
wood to a limited extent
only, so that the more
notable changes occur in
the bark. The canker is
sometimes superficial, the
attacks of the organism
being confined to the cor-
tical tissues. Attacks on
the wood of old limbs are
not frequent, but on twigs FiG. 35. HISTOLOGICAL CHANGES IN DISEASED WOOD

oO 0 \O/
KoTOCAoKE

i 5 Cross section of part of apple twig, showing brown deposit in
the wood 1S subject to wood fibers and wood parenchyma cells. Mycelium is also shown

common invasion by the 2 ol gen eae should be noted that none is found
parasite. In cross and lon-

gitudinal sections the first and the second, and sometimes the third,
layers of wood, and even the pith, are discolored. Closer examination
shows the mycelium to be very abundant within the vessels of the xylem
and in the woody parenchyma. In this region the characteristic brown
deposit is found, but is located chiefly in the cells of the medullary
rays and the wood parenchyma. Inoculations on young apple trees in
the greenhouse with the ascospore strain (no. 82, from apple) show that

II4 BULLETIN 379

there is a streak developed in the outer layers of wood (Fig. 34), just as
in the twig blight on chestnut oak, Quercus prinus, as reported by Ingram
(1912) and noted subsequently by Rankin (1914). The streak is due to
the discoloration of the cells, not to the presence of the mycelium
(Figs. 35 and 36). One has only to examine longisections through the
streak to be convinced that the hyphal threads do not grow in strands
and are not otherwise arranged so as to give such an appearance to the
tissue.

In the case of the more superficial cankers the ingress of the fungus is
cut off from the healthy tissue by the development of a cork layer (Fig. 37).
Such lesions reveal in section the presence of a layer approximating the
normal periderm, with which it is continuous and which reacts the same
with safranine and with a chloro-
phyll solution. These cells in their
final state are suberized.

The layer originates by the di-
vision of cells of the cortical paren-
chyma. The sclerenchyma fibers
are not changed. If the layer
comes in contact with a group of
sclerenchyma fibers it is inter
rupted. The more recently affecte
cells—that is, those nearest the
margin of the lesion—show a red-
dish tinge with safranine, ind1-

FIG. 36. HISTOLOGICAL CHANGES IN cating slight suberization through-

DISEASED WOOD out the region. Later, evidence
ing Mosont is wonly demine, Mucdian i Ofethe cork: layer iss toumdag eat
Fedintte pe sen ee beyond the infected zone. Walls
are laid down to form rectangular cells characteristic of the final
cork ‘layer and of the normal periderm. At this time they do not take
the safranine, indicating that suberization has not begun. Such sections
stained with chlorophyll solution also show no suberin reaction.

A later examination of the marginal layer between healthy and diseased
tissue stained with safranine will reveal three distinct and characteristic
zones, as follows (enumerating entad): a red layer of three or four suberized
cork cells; a colorless layer of about two non-suberized cells, rectangular;
and a third layer of about two smaller cells of the same shape bearing a
brownish deposit, making a distinct brown line. Many slides show the
reverse relation with respect to the suberized and cellulose layers; the
colorless layer, composed of cells with cellulose walls, may lie next to the
diseased tissue, and the cells with suberized walls next to the brown line.

Brack Rot, Lear Spot, AND CANKER OF POMACEOUS FRUITS 115

This raises the question as to which cells are suberized first. The assump-
tion is that those cells nearest the diseased zone are suberized first. This
would be expected, in such a case, where response to injury is made by the
host. But this scarcely explains the cases in which the colorless layer
borders the affected tissue. In these cases, however, the brown line
is not so distinct as described above, and often is not in evidence; so that
this may stand as a younger stage in the formation of the cork layer.
The cells of the suberized layers do not react alike when stained with
safranine. A row of cells in the center is the darkest, the color shading
off on both sides, perhaps
indicating the amount of
suberization.

Fhe majority of the cells
of the layer are densely
granular, are thin-walled
at first, and possess large
nuclei. These have the
characteristics of- rapidly
dividing cells.

A section through a
canker having a crevice at
its margin shows that the
break follows the brown
line. The dead tissues on
the one hand shrink, while
the living; normal part in-
creases in diameter by
growth, exerting tension on _ p,,

- 37. HISTOLOGICAL CHANGES IN DISEASED

all tissues of the bark, and BARK
Zt Showing brown deposit in the medullary ray cells and
the break results: It ap- 7.00 5S orci

, which cross at right angles resulting in
pears that the cells making a stratified appe nee in the phloem. Below the diseased

region is seen the cork layer
up the brown line are the
weakest, and thus they mark the line of separation of the diseased
from the healthy tissue.

Along the marginal layer diseased pockets occasionally are formed which
extend into the healthy tissue. Such areas are always in the region of a
group of sclerenchyma fibers. A cork layer surrounds the pocket. Cross
sections may be cut so as to include only a portion of one of these pockets,
making them appear as internal, separate infections. Serial sections,
however, always reveal their connection with the originally infected tissue.

In the diseased region are found the same stratified layers as mentioned
in the survey of the normal secondary cortex. But in the affected areas

116 BULLETIN 379

both the cells of the medullary rays and the phloem parenchyma stand
out very prominently, being filled with the brownish deposit. The
remainder of the old phloem elements, the sieve tubes, companion cells,
and sclerenchyma fibers, are not discolored at all. (Fig. 37.)

The brown mycelium of the fungus is found very abundantly throughout
the diseased area. It is intercellular, except when it encounters the xylem
and the hard sclerenchyma fibers; it 1s not easy to say just what the
relationship is with respect to hard sclerenchyma fibers. It is noted else-
where that the hyphe are found within the tracheal tubes. The threads
for the most part pass up and down the stem. ‘This is in accordance with
the external symptoms of a lesion. It has been stated previously that
where the cork layer encounters a group of sclerenchyma fibers it is inter-
rupted, and the fungus breaks through the barrier as laid down by its
host. There is no evidence that the suberized cells are ever penetrated.
Mycelium is found advancing through the layer at points where the
sclerenchyma fibers cross it, a discoloration precedes the hyphe, and
almost before the threads get into the healthy tissue the latter is changed
in its normal color. Very soon after is found evidence of a secondary
cork layer, which usually branches from the primary layer at some point
beneath the point of secondary penetration. This extends around the
newly affected region, finally passing above to the normal periderm.
Repetition of this process, accompanied by the formation of crevices at
each successive cork layer, results in the concentric lines or cracks so
characteristic, externally, of the lesion. The drying out and death of the
cells results in their collapse, and the affected part shrinks.

CONTROL

BLACK ROT
EXCLUSION BY LEGISLATION

As previously noted (Evans, 1910), the British Government at Cape
Colony has legislated against black rot. Importers are warned that,
under a government notice of 1908, all consignments of pomaceous fruits
found infected with this organism to the extent of one per cent and upward
will be destroyed on arrival at the Colony or returned to the consignor.

SPRAYING

It was suggested by Sturgis (1893 b) that spraying in August and
September would prevent black rot of quince. The following year the
same author (1894) found that a 0.03-per-cent solution of copper sulfate
is fatal to the fungus. More recently Waite (1906:19) recommends the
same treatment as for apple scab. Wolf (1913) concludes from experi-
ments conducted in Alabama that bordeaux 4—4-50, applied as follows,
will be effective: the first spraying, about July 15, when the disease is just

Brack Rot, Lear Spot, AND CANKER OF PomMacEous FRuITS 117

appearing; the second, two weeks later. This schedule gave satisfactory
control, the sprayed fruits showing less than one per cent diseased on
certain varieties. Control was less complete on Black Ben Davis, which
exhibited from ten to fifteen per cent of black rot. Lime-sulfur was found
to be wholly ineffective under southern conditions in rgr2.

It should be remembered that frequently infections follow the work of
the codling moth, and, as stated by Clinton and Britton (1910), the
control of this insect lessens the amount of rot starting at such centers.
The work heretofore described indicates that certain insects carry the
spores; it is therefore important to consider the control of these pests.

HANDLING OF FRUITS

It is apparent from the life history studies that spores of the black rot
organism are present in the orchard at picking time and are carried into
storage. It has also been learned that the fungus effects penetration only
through injured tissue. Consequently one factor in obtaining apples of
good keeping quality is the elimination of mechanical and other injuries
to the fruit; the occurrence of black rot in storage is undoubtedly connected

with the handling methods in use in the orchard.

e
STORAGE

It has been found by Lamson (1902:81), and subsequently by Eustace
(1908), that the temperature of the storage room should be about 31°
(iO) Bye 1, (Sais tho) args C.). Higher temperatures allow growth of the
fungus. It is important to note that when apples are stored in barrels,
about one week is required for the temperature of the center of the
receptacle to become equal to that of the storage room.

LEAF SPOT
SPRAYING

It seems that Alwood (1892) was the first to advocate the use of sprays
for leaf spot. He recommends two applications, as follows: the first,
just as the petals have fallen from the apple, using bordeaux mixture
4-5-50; the second, about twenty to twenty-five days later. The recom-
mendations of later writers differ in number of applications and in type
of fungicide. It is very apparent that the number of sprayings in a given
year will depend on the character of the season. Ordinarily two or
three applications are necessary, according to Brooks (1909, and 1912,
aandb) and others. In certain seasons of considerable rainfall additional
sprayings may be necessary.

As previously noted, in some districts at least the leaves are infected
shortly after they unfold from the bud, and infections may continue through-
out the spring according to Brooks (1909:124). Later Brooks and De-
Meritt (1912: 188) conclude that the period of infection extends throughout

118 BULLETIN 379

the middle of the summer. The number of applications then to be made
will depend on the character of the season and the abundance of spores
present.

In some sections of the country where apple scab also is to be combated,
the regular scab sprayings have been generally recommended as sufficient.
These are given by Wallace (1913: 589-500) as follows: the first, when
the blossoms show pink; the second, after the blossoms fall; the third,
two or three weeks later. If later scab sprayings are necessary, the
leaf spot will be controlled. Scott (1906:33) states that the disease
may be controlled in connection with the treatment for bitter rot; for
’ the latter disease he recommends from four to six applications of bordeaux
mixture, made at intervals of two weeks beginning about six weeks after
the trees blossom.

Apparently bordeaux mixture has been most commonly employed
for leaf spot. Brooks (1912 b:15) maintains that it is the most effective
fungicide for apple diseases, but points out that an objection to its use
lies in the fact that spotting of the foliage and russeting of the fruit are
likely to occur if showers follow its application. The spots produced on
tht leaves resemble those caused by the fungus. For leaf spot alone,
Brooks (page 8 of same reference) finds that self-boiled lime-sulfur best
holds the disease in check.

Lime-sulfur is regarded by Brooks (1912 b) as a satisfactory substitute
for bordeaux, and in a later publication Brooks and DeMeritt (1912)
show that commercial lime-sulfur at a strength of one gallon to twenty-five
gallons of water reduced the infection from about 95 per cent to 26 per cent.
When used at a strength of one gallon to fifty gallons of water, the lime-
sulfur was found to be less effective. Brooks considers this fungicide
about as efficient as bordeaux, and, because of the injury from the latter,
lime-sulfur would appear the more desirable. :

CULTIVATION

Brooks and DeMeritt (1912) have observed marked contrast between
the amount of infection in sod and in cultivated orchards. They record
the former as showing 0.79 spot per leaf, whereas in the latter there was
only 0.47 spot per leaf. They say (page 189 of reference cited):

The trees had been treated alike in every other respect and were of equal vigor when
the experimental worl was begun; it was, therefore, evident that cultivation had reduced
the disease almost one-half. This reduction was probably partly due to the fact that the
leaves were plowed under on the cultivated plots, but the lack of general vigor in the
trees on the sod plots was apparently partly responsible for the difference.

CANKER
HISTORICAL AND INTRODUCTORY
The control of cankers has been a matter of consideration for some time.
Nearly three centuries ago Parkinson (1629:550) recommended surgical

Brack Rot, Lear Spot, AND CANKER OF Pomaceous FRUITS 119

methods together with a wound dressing of vinegar. Similar advice is
given by Harrison (1823:342), who suggests a dressing of soot, water,
and train oil. He recommends drainage of the soil in severe cases.

In more recent times, beginning with the appearance of the work of
Paddock (1899 b), the recommendations are all essentially of the same
nature. The employment of the common methods of orchard manage-
ment — cultivation, fertilization, pruning, and spraying —is recom-
mended, in order to promote general vigor. Keeping the trees in good
growing condition is claimed to be essential (Warren and McCourt, 190s).
Spraying to protect the bark is frequently recommended (Bethune, 1909: 30,
and others), while scraping the bark and applying a wash is suggested
by Paddock (1899 b:190) and others. Pruning of diseased limbs and
the growing of a new top is being practiced by some growers.

The control measurés more commonly employed by the growers of
New York State are pruning and spraying; other measures, as determined
by circular letters and personal observation, are surgery, cultivation,
fertilization, and mulching. The success of these methods varies and
seems to depend on the vigilance with which the grower pursues the
disease.

SURGICAL METHODS :

PRUNING. In pruning for the control of canker, two methods may
be employed: the limb may be cut from the tree entirely, or the cankered
bark may be removed. In either case a wound will result and the appli-
cation of a dressing becomes essential.

Removal of limbs—— The question frequently arises, when shall only
the canker be cut out, and when is it necessary to remove the limb? No
general rule can be laid down, but each case must be examined carefully
and procedure taken accordingly. If the limb is large and productive,
its removal should be postponed. This is commonly the practice. But
to wait until the limb is not producing satisfactorily usually means that
the canker will aid in bringing the branch to destruction. In such cases
it is advisable to prevent the loss by eradicating the cankered spot by
surgery.

If the limb is not producing, whether large or small, its removal for
the purpose of eliminating the fungus is the alternative. The cut should
be made so that another limb, or water sprout, may be allowed to grow
in the approximate space left by the part removed. This method of
treating the New York apple tree canker is employed in certain orchards
along the Lake Ontario belt in this State. One grower is very successful
in this measure of control. This, with protection from new infections
by careful spraying of the entire tree — trunk and limbs — renders even
the highly susceptible Twenty Ounce variety practically free from canker.

120 BULLETIN 379

Grafting of stubs ieft by the pruning of the affected parts of limbs
is occasionally practiced. This may be justified in certain cases, although
as a rule it should be supplemented in the main by the method just
described.

Removal of diseased bark.— The cutting out of cankers is a method
to be employed when the grower is satisfied that the value of the limb
warrants it. An attempt to remove all kinds and sizes of cankers from an
infested orchard without regard to such a consideration is likely to result
in the discouragement of the orchardist with the whole undertaking.
The equipment necessary for use in the removal of cankered bark consists
of a drawshave and a farrier’s knife. The limits of the diseased area are
ordinarily determined by making an external examination of the canker.
Where this method is not reliable, small bits of the outer bark may be
removed, following the line of the discoloration until the limits are deter-
mined. Similarly the depth of the canker is defined.

The shape of the cut will vary somewhat with that of the canker to be
removed. So far as possible, the wound when finally finished should be
lenticular in form. This will facilitate callus formation. If the wound is
rectangular the upper and lower edges heal more slowly. The edge of
the wound should be perpendicular to the long axis of the limb, for cuts
made at a slant will result in a certain amount of dead cortex, which is
undesirable from the standpoint of new infections. A possible exception
to this method of trimming the margin is to be found at the lower end
of the wound. Here the edge should be slanting enough to permit
drainage of moisture.

WOUND TREATMENT. It is frequently advised that the wound should
be disinfected and protected. The latter is certainly commendable
practice, but whether the former is necessary will depend on the nature
of the wound dressing.

Wound disinfection — If the dressing itself is a disinfectant, a special
disinfectant will not be necessary. In case one is needed, mercuric
chloride at the usual strength (1-1000), or copper sulfate (1 ounce to 1
gallon of water), is most commonly used.

Wound protection.— The necessity of a protective covering for wounds
is twofold: to check the weathering of the wound, and to prevent the growth
of bacteria and fungi. It follows, then, that the fundamental requirement
of a wound dressing is that it should be a preservative and a pre-
ventive. Briefly, then, the dressing should have antiseptic qualities, and
should be fluid, reasonably inexpensive, and easily prepared and applied;
it is essential that it should give complete covering; it must be impervious
to air and water, must be durable, and must not injure nor kill the
tissues nor interfere with the healing process.

Buack Rot, Lear Spot, AND CANKER OF POMACEOUS FRUITS tr2t

The preparations now most commonly used are paint, tars, and
asphaltum. In some cases commercial tree paints are employed. It is gen-
erally agreed that paints are an inefficient covering, whereas asphaltum
once applied gives the desired protection. Asphaltum, however, is more
difficult to apply. This is particularly true if the asphaltum used is
rendered liquid by heat; if it is dissolved in gasoline it is more easily pre-
pared and hence more available. The combination of asphaltum and
gasoline has been applied rather extensively in the orchard of Fred Hazle-
ton, at Leroy, New York, and from all appearances is commendable.

The writer has used coal tar for the past three years with good success.
This is a residual tar derived in the manufacture of artificial gas from coal.
According to Lunge (1909), tars may vary even from the same materials,
depending on the temperature used in the distillation, the shape of the
retort, and other factors. The use of coal tar as a wound dressing has
been recommended to growers of the State, and some have complained of
injury to the healthy tissue from its use while others report it as an appro-
priate material. Many cases of injury have been found to have resulted
from the use of creosote, but not from coal tar. The pruner must dis-
tinguish between the two materials. The writer has never seen any cases
of injury from coal tar on apple trees, and it has been used successfully
on peaches by Jehle (1913). It is interesting to note a quotation from
Des Cars as given by Bailey (1907: 111-113):

The application of coal tar should not be made except with considerable caution
in the treatment of wounds on drupaceous fruits (cherries, peaches, plums, etc.), and
especially on the plum tree. It has often been observed that the bark of fruit trees
of this class has suffered from the application of coal tar. This is not the case, however,
with pome-bearing trees (apples, pears, etc.); to these coal tar may be applied with
perfect safety.

Card (1897:9) reports experiments in pruning in which he tested various
materials for protecting wounds. He says of coal tar: “‘ Coal tar, how-
ever, seems to have been a positive hindrance to the healing process, not
one wound having been reported as healing extremely well, while the
majority are reported as healing only fairly well.’’ As a comment on this
remark, Bailey (1907: 113) says: “It is not said, however, whether the tar
injured the tissues, or whether the apparent results may not have been
due to the position and character of the wound quite as much as to the
dressing. In my own experiments . . . ._ tar did no damage.”

In view of the complaints made of injury from the use of coal tar, it
occurred to the writer that this substance varied sufficiently in different
parts of the State to account for the injury, if any ever occurred. Samples
were obtained from the gas plants in the following cities in New York:
Syracuse, Owego, Batavia, Rochester, Ithaca, Lockport, Buffalo, Albion,
and Geneva. These samples were applied to wounds of mature apple

122 BULLETIN 379

trees on the farm of Dr. Johnson,.at Leroy, New York, in*August, 1912.
Examination at intervals during the growing seasons of 1912 and 1913
showed equally good healing and no injury. Another orchard, near
Batavia, New York, owned by Chapin & Son, has been extensively treated
with coal tar, with results similar to those just described. The writer has
applied coal tar to Northern Spy, Baldwin, and Hubbardston apples in
an orchard at Byron, New York, and no detrimental effects have been
observed. In some cases the wound has been disinfected by the use of
mercuric chloride (1-1000), but no difference in the efficiency of protection
was observed between wounds so treated and those not disinfected. The
writer feels safe in recommending the use of coal tar without previously
disinfecting the wounded surface.

The cost of canker treatment — that is, the removal of diseased bark
and the application of a dressing —is not an easy matter to determine.
Where it is done extensively the grower usually does the work along with
the regular pruning, so that the cost of canker treatment alone can hardly
be separated from that of the whole operation. In an apple orchard at
Leroy, New York, careful work was done in 1912 by A. S. Davis. The
orchard contained gso forty-years-old trees. The orchard had been
neglected for several years, and dead limbs, cankers, collar rot, and heart
rot were abundant. Mr. Davis furnishes the following figures:

Costiomtrimimin ge he ccc ena en ieee reas $407.90
Coal tar, 40 gallons, at 20 cents a gallon Sy Maker decy toca oe 8.00
Corrosive sublamatesa 2 ane eee eee a5
Applying? tate we endef cet Gan He, aoe ucla le ee tebe Nias 30.00
Removal and destruction of brush................ 54.70

Totalle Vc cies Ot: a eae $501.35

The following data are taken from a similar orchard at Batavia, New
York:
Miscellaneous data

Number of treest han a ane Aen me ete 360
Age:Of GreeS), 21... ars Sons sure aac Cet eae 30 years
Cost
Labor, 348 hours, at 25 cents an hour......... $87.00
Coal tar, ro gallons, at r5 cents a gallon....... 1.50
Corrosive sublimate...... PEC Op ranean ocsbase 5 iso) ©
TOCA asic ccc yotatel chord. oo ee eale ee oss Spee ea $89.00

Tt is seen that the average cost of the work in the Leroy orchard is
about fifty-two cents a tree. It must be borne in mind that the orchard

Brack Rot, Lear Spot, AND CANKER OF PomAcEouS FRUITS 123

had not been pruned in several years, which accounts in part for the
high cost of the work. In the Batavia orchard the average cost is approx-
imately twenty-five cents a tree. These figures do not represent the cost
of treating the cankers alone; this process itself would be considerably
less than either of the above figures.

WOUND HEALING. Wound cork— According to Hartig (1894:225),
whenever the living phellogen is injured a new zone of phellogen, or
cork, which is continuous with the cork layer along the edge of the wound,
is formed from the uninjured cells which are situated deeper in the
cortex. The cortical parenchyma, which lies beneath the periderm,
possesses sufficient power of cell division to enable it to keep pace with
the increasing thickness of the stem. But in the case of the wound its
reproductive capacity is confined to the development of a periderm close
beneath the surface of the exposed tissues. Its formation does not depend
on the season of the year, but it may be formed even in winter.

Wound wood.— Hartig (1894:228) states that wood exposed by a
wound has the power of producing new cortex and new wood when the
cambium is active and when the cambium layer and young wood are
protected from drought. In such a case, regeneration of the covering
layers is effected. The cambial region consists of embryonic bast and
wood, which is capable of growth and ultimately of a certain amount
of differentiation. The wood thus formed is termed wound wood.

Callus — Callus may be developed when the cambium has dried up
or when it is absent from the surface of the wound. Its formation proceeds
from the edge of the wound, beginning in the cambium. Hartig (1894:
231) states that it is a purely mechanical process and results from the
reduction of the bark pressure on these tissues. There is always a certain
amount of tension in the cortical mantle, whereby a considerable pressure
is exerted on the cambium. Should this pressure be locally reduced by
a wound’s reaching the wood, the processes of cell division and growth
are accelerated not only along the edges of the wound but also at greater
distances. The callus cushions advance from the edges of the wound,
finally coming in contact and coalescing. This coalescence is retarded
if the callus is clothed at an early stage with dead bark.

It has been noted that wounds made in cutting out cankers should be
pointed in order to permit rapid healing. In this connection Hartig
(1894:232) states that the formation of callus proceeds more vigorously
in case of a longifudinal incision than when the incision is transverse.
This is explained by the nature of the pressure by the bark in consequence
of peripheral enlargement of the stem. The pressure here acts like that
of a barrel hoop on the staves, and so callus develops more rapidly along
the lateral margins of the wound. In this connection the question of

124 BULLETIN 379

slitting the lower edge of the callus arises. Reasoning from the data
regarding the development of the callus, it seems advisable to practice
this operation each year; this prevents the callus from bunching, and
stimulates it to more ready occlusion of the wound.

SPRAYING

The effectiveness of spraying for canker is a question frequently raised.
It is the belief of the writer that spraying as a preventive, but not as
a cure, is worthy of attention. It is true, however, that growers report
cases of curing canker by spraying. The fungus mycelium is protected
by the bark; hence sprays will not reach it, and eradication of the fungus
from a given lesion by spraying seems highly impossible. Spraying to
protect healthy bark from infections would certainly appear advisable,
but the data at hand are somewhat conflicting. The writer recalls an
orchard in which canker does not occur. The trees are sprayed carefully
each year, according to general recommendations for apples. Some of
the trees are Twenty Ounce, but they are free from the disease. The
limbs are kept coated with spray throughout the summer, and as late
as the middle of August these trees are still covered. In contrast to this
orchard, another is recalled which is severely affected with canker, yet
the trees are given the regular sprayings. The difference in these cases
may be accounted for by the lack of thoroughness of the spraying in
the second orchard. Since protection is the principle involved in this
method of control of canker, the success of any attempts in this direction
is determined by the completeness of the covering.

GENERAL CONSIDERATIONS
The destruction of rubbish about the orchard is no new suggestion.
Peck (1879:21) recommends that affected fruit should be removed from the
orchard and destroyed. The destruction of fallen leaves is recommended
by Alwood (1892). Sheldon (1905) and others suggest picking rotted
fruit before the fungus spores mature in the case of quince black rot;
Sheldon adds that this might not be possible with apples because of the
size of the trees. In Alabama, however, Wolf (1913),as has been previously
noted, controlled the disease by spraying. The opinion is held by Brooks
and DeMeritt (1912:189) that affected leaves should be plowed under,
while clean cultivation is the recommendation of Reed, Cooley, and
Rogers (t912:5). The removal and burning of affected limbs is advocated
by Bethune (1909: 30) and others.
The ability of the fungus to pass from one part of the apple tree to
another only adds to the sources of inoculum, so that sanitary measures
become of special importance.

Brack Rot, LEAF Spot, AND CANKER OF PoMACEOUS FRUITS 125

ORCHARD MANAGEMENT

The value of careful handling of fruit to prevent injury has been
emphasized. This is based on the principle that the causal organism
is a wound parasite. The same care should be exercised with reference
to the bark of the tree; injury should be avoided whenever possible.
Injuries to bark are likely to result from cultivating implements and
harness, the careless handling of ladders while picking, and climbing
over the trees with rough-soled boots. The importance of guarding against
such orchard practice lies in the fact that cankers begin in just this sort
of place.

It has been mentioned that the fungus follows winter injury. As
a protection against winter injury, Reddick (1912:37) advocates early
plowing in the spring, and cultivation to give the trees the advantage
of conserved moisture; he recommends that cultivation should cease not
later than August 1, in order to start the trees into maturation. Cover
crops, to take up excess moisture in the autumn, should be sown. Soil
drainage in low ground, and a good circulation of air, are important
considerations.

When it is desired to grow varieties that are susceptible, the canker
difficulty may be obviated to a considerable extent by working over the
larger limbs of more resistant varieties to the one desired. This has
been done with apparent success in a few instances. The difficulties
involved are that pruning must be done every year to remove all sprouts
from the stocks, and that renewal of old branches cannot be effected
so readily. Such a treatment also throws the bearing area higher into
the air, so that in the case of erect growers, such as Twenty Ounce, thorough
orchard operations are made more difficult.

RESISTANT VARIETIES

Since certain varieties of the apple — for example, Esopus and Twenty
Ounce — are more susceptible to canker than are other varieties, the
growing of other varieties will undoubtedly render the problem of control
less difficult. Twenty Ounce, however, is one of the most satisfactory
fall varieties for commercial planting in New York State. The question
therefore arises, whether the orchardist should sacrifice the growing of this
variety in the hope of escaping the problem of canker control. The
evidence at hand indicates that if a grower wishes to raise Twenty Ounce,
his success in keeping the trees free from canker will depend on his efforts.
Observations warrant this opinion. It is true that, as stated by Warren
and McCourt (1905), ‘“‘something more than thrifty growth seems to be
necessary in order to prevent the destruction of the Twenty Ounce ’’;
so that vigor in itself should not be given too much dependence. Well-

126 BULLETIN 379

cared-for trees of this variety are often severely cankered. It is assumed
that the trees must be in a thrifty ‘condition in order to give the best
results, but the control problem does not end here, for vigor does not estab-
lish nor maintain resistance.

AN ENEMY OF THE PATHOGENE

Potebnia (1912)® reports an interesting case of a fungus, Helico-
myces Sphaeropsidis Potebnia, living as a parasite within the conidia of
Sphaeropsis pseudodiplodia [= Physalospora Cydoniae]. Infection takes
place when the host (the conidia of Physalospora Cydontae) is in the Macro-
phoma stage. He notes a similar case reported by Japp, in which Helt-
comyces niveus Bres. & Japp is parasitic on Diplodia inquinans West.,
and states that in Japp’s herbarium specimen all pycnospores in the
infected pycnidia were killed by this parasite.

BIBLIOGRAPHY
(Anonymous)
1899a The appe canker. Country gent. 64:88.

Briefly summarizes the works of Waite and Paddock.

1899 b The apple canker. Country gent. 64:208. Illustrated.

The illustration is a text figure, and the author contends that it is the first figure of —
the disease published.

1899 c Perhaps apple canker. Country gent. 64:248.

Areply to an inquiry concerning the apple injury which is regarded as caused by Sphae-
ropsis Malorum. Remedy suggested.

Alderman, W. H., Giddings, N. J., and Rumsey, W. E.
1913 Orchard spraying. West Virginia Univ. Agr. Exp. Sta. Cire. 7:
TPs), Mee, TS)
Mention black rot, leaf spot, and canker, and suggest control measures.

Alwood, W. B.
1892. Brown spot. Jn Four diseases of the apple, and treatment of
same. Virginia Agr. and Mech. Coll. Agr. Exp. Sta. Bul.
THES OMOL:

Describes a leaf disease and uses the name brown spol. Notes three successive out-
breaks in a summer. Questions whether Phyllosticta pirina is the cause.

1893 Injurious insects and diseases of plants with remedial measures i
for the same. Virginia Agr. and Mech. Coll. Agr. Exp. Sta. -
Bul. 24:1-40. Illustrated.
The apple orchards of Virginia said (p. 24) to suffer chiefly from two foliage diseases
one of which is called brown spot, attributed to the attacks of Phyllosticta pirina.
1898a The leaf-spot disease of apple, Phyllosticta pirina Sacc., and
several unrelated forms occurring therewith. Amer. Assoc.
AGKGisiGl, leiole) “ssi.

Records the following fungi occurring with Phyllosticta pirina Sacc: Sphaeropsis
Malorum Peck, Hendersonia Mali, and an undetermined species. :

8 Translated by C. D. Sherbakoff, formerly of the Department of Plant Pathology at Cornell University.

Brack Rot, LEAF Spot, AND CANKER OF PoMACEOUS FRUITS 127

1898 b On the occurrence of a yeast form in the life cycle of the black
rot of apple, Sphaeropsis Malorum Peck. Amer. Assoc. Adv.
Sci. Proc. 47: 422.

Records the discovery of a yeast form occurring in cultures of this fungus, which
qn isolation and reinfection on the fruit of apple produced the common fruiting
bodies of Sphaeropsis Malorum.

1902 Orchard studies—XV. The bitter rot of apples. Virginia Agr.
Exp. Sta. Bul. 142:250-274, pl. 1-4.

States (p. 257) that Sphaeropsis Malorum Berk. invades fruit already decaying from the
attacks of the bitter rot fungus.

Alwood, W. B., and Price, H. L.
tgo2 Orchard studies—V. Report on crab apples. Virginia Agr.
Exp. Sta. Bul. 132:3—14, fig. 1-4.

Note (p. 6) that certain varieties are especially subject to the black rot canker (caused
by Sphaeropsis Malorum).

Arnaud, G.

1912 Notes phytopathologiques. 1. Sphaeropsis pseudodiplodia. Mont-
pellier (France) Ecole Nat. d’Agr. Ann. 12:5-17, fig. 1-5.

Discusses the fungus as it occurs on several different plants. Notes the variable
morphology of the organism and reports the discovery of an ascomycete associated
with the pycnidial form. The ascomycete is named Physalospora Cydoniae and is re-
garded as probably the perfect stage of Sphaeropsis pseudodiplodia.

Arthur, J. C. 2
1885 Quince rot. Jn Report of the Botanist. New York (Geneva)
Agr. Exp. Sta. Ann. rept. 3:372.

Describes symptoms, ae proves the pathogenicity of the fungus (which he calls Sphae-
ropsis Cydoniae C. & E.) on quince fruit.

Baccarini, P.
1890 Note patologiche. Ital. nuovo giorn. bot. 22:64-70.

Reports Sphaeropsis Malorum on pears, apples, and peaches in storage. Discusses
sclerotia and pycnidial development.

Bailey, L. H.
1907 The healing of wounds. Jn The pruning-book, p. 76-132, fig.
68-110.

Gives a chapter on the healing of wounds, taking up the nature of wounds, suggestions
for the pruner, dressings for wounds, making cuts.

Baldwin, C. H.
1912. Black rot. In Some important diseases of apple. Indiana State
Entomologist. Rept. 5:249-252. Illustrated.
Gives notes on black rot, leaf spot, and canker.
1914 Black rot (New York apple-tree canker and apple leaf spot).
In Apple diseases. Indiana State Entomologist. Rept. 7:
150-152. Illustrated.

Describes the nature of the injury.

Bary, A. de
1887 Comparative morphology and biology of the fungi, Mvycetozoa,
and bacteria, p. 1-525. (Translated by H. E. F. Garnsey
and I. B. Balfour.)

Discusses (p. 247) types of pycnidial formation in general.

128 BULLETIN 379

Beach, S. A.
1912 Black rot.. In Spraying practice for orchard and garden. Iowa
Agr. Exp. Sta. Bul. 127:50-51. Illustrated.

Black rot observed to occur on some of the summer and early fall varieties.

Beach, S. A., Lowe, V. H., and Stewart, F. C.
1899 apie tree canker. Also, Leaf spot. In Common diseases and
insects injurious to fruits. New York (Geneva) Agr. Exp.
Sta. Bul. 170:382-384.

Describe canker, caused by Sphaeropsis Malorum Peck, and leaf spot, due to Phyllosticta
spp., with recommendations for control.

Beal, W. J.
1898 Diseases of the apple. Michigan State Hort. Soc. Ann. rept.
27: 174-183, pl. 1-4.

Discusses ee I 78) symptoms of black rot of apples, and compares it with soft rot (caused
by Penicillium expansum Link).

Berkeley, M. J.
1836 Sphaeria Malorum. In Hooker’s English flora, p. 257-258.
Describes the fungus Sphaeria Malorum Berk.
1860 Sphaeropsis Malorum B. Jn Outlines of British fungology, p
316.

Changes the generic name of the fungus from Sphaeria to Sphaeropsis.

Berlese, A. N., and Voglino, P.
1886 Macrophoma Malorum (Berk.) Berl. & Vogl. Cited in Sac-

cardo’s Syll. Fung. t0:197. 1892. From Veneto-Trentina
Soc. Atti. 1886: 184.

The authors divide the genus Phoma into Macrophoma and Phoma, the basis being the
length of the pycnospores; Phoma Malorum (Berk.) Sacc. becoming, as they believe,
Macrophoma Malorum (Berk.) Berl. & Vogl.

Bethune, C. J. S.
1909 Fungus diseases and insect pests. Also, Cankers on apple trees.
Ontario Agr. Coll. and Exp. Farm. Ann. rept. 34: 26-32.

Reports (p. 29) that cankers do great damage along the north shore of Lake Ontario.
Says (p. 20) that spores of Sphaeropsis Malorum are carried by the wind.

1910 Black rot canker (Sphaeropsis Malorum). Ontario Agr. Coll. and
Exp. Farm. Ann. rept. 35:35-36.

States that black rot canker apparently can be successfully controlled by pruning out
dead branches, cutting out cankers, and coating the bark with spray.

Bommer, E., and Rousseau, M.

1885 Blorule mycologique des environs de Bruxelles, p. 3-353.
Sphaeropsis Malorum Berk. is listed (p. 257) on fallen apples.

Brooks, Charles

1907. Diseases of the apple. Jn Seventeenth and eighteenth annual
reports. New Hampshire Coll. Agr. Exp. Sta. Bul. 129:
207-2 700sple 5.

Records black rot and cankers due to Sphaeropsis Malorum Berk. as common; records
leaf spot due to Phyllosticta pirina Sacc. and P. limitata Peck as serious, with little
or no effect on it from spraying. States that majority of apple limb cankers are
caused by Sphaeropsis Malorum Berk., and that few of the orchards visited did not
show the disease,

Brack Rot, Lear Spot, AND CANKER OF PoMACEOUS FRUITS 129

1909 _ Black rot, canker, and leaf spot. Jn Some apple diseases. New
Hampshire Agr. Exp. Sta. Bul. 144: 123-126, fig. 20-24.
Discusses occurrence, symptoms, etiology, and control of black rot, canker, and leaf
spot. Lists the following fungi as associated withthese diseases: Sphaeropsis
Malorum, Coniothyrium pirina, Coryneum foliicolum, Alternaria sp., and one of the
Tuberculariae.

t912a_ Black rot, canker, and leaf spot. In Some apple diseases and
their treatment. New Hampshire Agr. Exp. Sta. Bul.
157:17-20, fig. 20-24.

Maintains that black rot does considerable damage in storage. Outlines sprayings
which are said to be fairly effective for leaf spot.

1912 b Fungicides in the apple orchard. New Hampshire Agr. Exp.
Sta. Bul. 161:1—15.

Compares different fungicides for control of leaf spot.

Brooks, Charles, and DeMeritt, Margaret
1912 Apple leaf spot. Phytopath. 2:181-190, pl. 17, fig. 1-6.

Give an account of the etiology of leaf spot, paying particular attention to the morpho-
logical and biological variations in Sphaeropsis Malorum. Infection shown to occur
from the time the leaves unfold until the last of August. Cultivation, spraying, and
the removal of cankers given as the important control measures.

Brooks, Charles, Fisher, D. F., and Cooley, J. S.
1914 Apple rots. Phytopath. 4:403. (Abstract.)

List several species of fungi, including Sphaeropsis Malorum, which were isolated from
market and storage apples.

Bryce, P. I.
‘1915 Apple leaf-spot or black rot canker. Quebec Soc. Prot. Plants
from Ins. and Fung. Dis. Ann. rept. 7:86-90. Illustrated.

Gives an account of symptoms, varietal susceptibility, and control of the disease.

Bubak, Fr.
1909 Ein kleiner Beitrag zur Pilzflora von Niederésterreich. Ann.
myc. 7:59-62.

Sphaeropsis Mali (West.) Sacc. listed (p. 62) as collected on Pirus Malus in ‘“‘ Hohe
Warte” bei Wien.

Burrill, T. J.
1907 Bitter rot of apples: botanical investigations. Illinois Univ.
Agr. Exp. Sta. Bul. 118:553-608.

States that Sphaeropsis Malorum is sometimes associated with the bitter rot fungus in
cankers. The former organism said to follow the latter under Illinois conditions.

Burrill, T. J., and Blair, J. C.
1901 Apple fruit-rots. Illinois Univ. Agr. Exp. Sta. Cire. 37:(12
pages, unnumbered). Illustrated.

Special attention given to symptoms of black rot, caused by Sphaeropsis Malorum. Sug-
gestion that another species causes canker. Discussion on second and third pages.

Butler, O.
1912 Report of the Department of Botany. In Twenty-third and
twenty-fourth reports. New Hampshire Agr. Exp. Sta. Bul.
163); 10-17.

Mentions the work of Brooks, which appeared later in Phytopathology 2:181-190 and
was published jointly by Brooks and DeMeritt.

130 BULLETIN 379

Caesar, L.
1909 Black rot canker of apple trees. In Lime-sulphur wash. Part
II.— Practical and popular treatment. Ontario Agr. Dept.
Bul. 177:)59-61, fig: 16:

States that on leaves and fruit the disease is seldom serious, but cankers often do great
damage especially in Prince Edward County, Ontario.

1912 Black rot canker. Jn Our most troublesome orchard insects
and diseases. Ontario Fruit Growers’ Assoc. Ann. rept.
44:22, fig. 15.

Author is convinced that the fungus follows winter injury.

Card, F. W.
1897 Notes on pruning. Nebraska Agr. Exp. Sta. Bul. 50:1-10.

Concludes from experiments that lead paint is the best material for covering wounds;
grafting wax said to be the next best; coal tar found to prevent checking, but seemed
to hinder the healing process; pine tar and shellac reported as unsatisfactory.

Chase, W. W.
1913 Apple leaf spot. Jn Principal insects and diseases of the apple
in Georgia. Georgia State Bd. Ent. Bul. 38:40-41, pl. 6,
fig. 2.

Leaf spot caused by Sphaeropsis Malorum said to be one of the most destructive apple
foliage diseases in Georgia.

Chester, F. D.
1g01a Canker in apple and pear. Jn Pear blight and pear canker.
Delaware Coll. Agr. Exp. Sta. Bul. 52:6-8, fig. 4—7.

States that twigs and branches bearing pycnidia of Sphaeropsis Malorum Peck
are sources of infection.

1901 b Canker in the apple and pear. Jn Report of the Mycologist.
Delaware Coll. Agr. Exp. Sta. Ann. rept. 12: 43-46, fig. 4-7.
(Same as 1901 a.)
1902 Pear canker treatment. Also, Canker in apples. Jn Sundry
notes on plant diseases. Delaware Coll. Agr. Exp. Sta.
Bells Gis se, ey, Gop

Describes symptoms and control of canker of pear and apple caused by Sphaeropsis
Malorum.

Clement, F. M. .
1913 Winter injury in orchards. Quebec Soc. Prot. Plants from Ins.
and Fung. Dis. Ann. rept. 5: 24-26.

Says that frost wounds are made doubly serious if not treated to prevent the admission
of the spores of saprophytic fungi, especially those of the black rot fungus, with the
consequent development of apple canker.

Clinton, G. P.
1902 Black rot, Sphaeropsis Malorum Berk. Jn Apple rots in Ilinois.
Illinois Univ. Agr. Exp. Sta. Bul. 69:192-193, pl. B, fig. 2.

Sphaeropsis Malorum Berk. regarded as one of the chief causes of rotting of apples in
market.

1904 Black rot, Sphaeropsis Malorum Pk. In Report of the Botanist.
Connecticut (New Haven) Agr. Exp. Sta. Ann. rept. 27: 208,
SYP ao, jolls mat, Gh.

Black rot regarded as one of the commonest and most universal diseases of the apple.
Noted also on pear and quince.

Buack Rot, LEAF Spot, AND CANKER OF PoMACEOUS FRUITS 131

1907. Winter injury and canker, Sphaeropsis Malorum Pk. In Report
of the Botanist for 1906. Connecticut (New Haven) Agr.
Exp. Sta. Ann. rept. 30:310-311, pl. 17, a
A peculiar limb disease of the apple is doubtfully attributed to winter injury and
Sphaeropsis Malorum.
1915 Notes on plant diseases of Connecticut. Jn Report of the
Botanist for 1913. Connecticut (New Haven) Agr. Exp. Sta.
Ann. rept. 38 (1914):1-29. Illustrated.

Black rot noted on stored apples (p. 5).

Clinton, G. P., and Britton, W. E.

1910 Black rot, Sphaeropsis Malorum. In Tests of summer sprays on
apples and peaches in 1910. Connecticut (New Haven) Agr.

Exp. Sta. Ann rept. 33-34:590, pl. 21, b.
Authors report occurrence of black rot (due to Sphaeropsis Malorum) on summer and

stored winter varieties. State that the use of insecticides in keeping out codling
moth lessens the rot starting from this cause.

Cook, M. T.
1913 Report of the Plant Pathologist. New Jersey Agr. Exp. Sta.
Ann. rept. 33: 509-527.
Black rot of apple and quince, caused by Sphaeropsis Malorum, among the diseases
listed (p. 512) as most important and most common in the nurseries.
1914a_ Black rot of the apple and quince. Jn Some diseases of nursery
stock. New Jersey Agr. Exp. Sta. Cire. 35:13—-14, fig. 9.
Twig and leaf-spot forms of the disease very common in nurseries. It is advised that
diseased trees should never be set.
1914b Black rot (Sphaeropsis Malorum Pk.). Jn Most common
diseases of the year. New Jersey Agr. Exp. Sta. Ann. rept.
34: 799, 809.

Black rot of apples most severe on Red Astrachan, Star, Lawver, Smokehouse. Black
rot of quince reported as being very abundant and very severe.

Cooke, M. C.
1892 Sphaeropsis pomorum (Schwz.). Jn Sphaeriaceae imperfectae
cognitae. Grevillea 20:86.
Suggests that Sphaeropsis pomorum (Schwz.) [=Sphaeria pomorum Schwz.] is probably

the same as Sphaeropsis Malorum Peck, of which Phoma Malorum Berk., erected by
Saccardo, is possibly a younger condition.

Cooper, J. R.
1913 The control of canker in the orchard. Nebraska hort. 3:2: 1-2.

Black rot canker is ranked third in importance among cankers in Nebraska. The dis-
cussion of control measures is directed at the Illinois blister canker.

Corbett, L. C.
1900 Brown spot, frog eye. In Fruit diseases and how to treat them.
West Virginia Agr. Exp. Sta. Bul. 66:202—-204, fig. 2

Author considers frog-eye, or brown spot (said to be due to Phyllosticta Pees more
injurious than either blight or scab.

132 BULLETIN 379

Crabill, C. H.

1915 The frog-eye leaf spot of apples. Virginia Agr. Exp. Sta. Bul.
209 :3-16, fig. 1-5.

Author states that frog-eye leaf spot is the most prevalent of apple foliage diseases in
Virginia. The annual losses from the disease are said to be heavy in that State, but
systematic spraying has controlled the disease in a satisfactory and effective manner.
Symptoms are described. Etiological studies are tabulated, and from his experiments
the author concludes that frog-eye spots are initiated by Sphaeropsis Malorum. All
other fungi with which he deals are classed as facultative parasites, following S.
Malorum, or as pure saprophytes.

Cummings, M. B.
1909 Apple orchard survey of Niagara County. Cornell Univ. Agr.
Exp. ota: Bull 262):277—320, fig. 26-40.

Gives notes (p. 304, table 12) on economic importance of canker.

Dandeno, J. B.

1906 A stimulus to the production of cellulose and starch. Michigan
Acad. Sci. Rept. 8: 40-44.

Claims that the fungus Sphaeropsis Malorum stimulates the cells of ripe apple fruit to
form starch and.to thicken the cellulose walls. Suggests that starch is built up first
and then dissolved and built into cellulose, the process going on until the fruit is
mummified and dry, whereupon it is in a state of preservation.

Delacroix, G.

1903 a Surunchancre du pommier produit par le Sphaeropsis Malorum
Peck. Soc. Myc. France. Bul. 19:132-140. Illustrated.

Gives an account of the disease which, it is believed, appeared in France at least
as early as 1901. Discusses the morphology of the parasite and the relationship
of the mycelium to the tissues of limbs, mentions inoculation experiments, and
suggests control measures.

1903 b Sur l'identité réelle Sphaeropsis Malorum Peck. Soc. Myc.
France. Bul. 19: 350-352.

Reports the examination of the following type material: Sphaeropsis Malorum Peck,
S. Malorum Berk., Diplodia maura Cooke & Ellis, D. pseudodiplodia Fekl., and
Botryodiplodia Mali P. Brunaud. Concludes that S. Malorum, D. maura, and B.
Mali are all different, and that S. Maloruwm in France, S. Malorum Peck, and D.
pseudodiplodia Fckl. are identical. States that since D. pseudodi plodia was
described before S. Malorum, the latter name should disappear, and the new com-
bination S. pseudodiplodia (Fckl.) G. Del. is proposed.

Dickens, A., and Headlee, T. J.
Igii Spraying the apple orchard. Kansas Agr. Exp. Sta. Bul.
T7425 0-202, oe 1O:

Give an account of experimental work in the control of black rot by spraying. Bor-
deaux mixture and lime-sulfur were used on several varieties.

Douglass, B. W.

tg1o0_ Black rot. Jn Plant diseases. Indiana State Entomologist.
Rept. 2 (1908-1909) : 135.

The disease is briefly described.

Duggar, B. M.

1909 Black rot and canker of pomaceous fruits. Jn Fungous diseases
of plants, p. 303, 350-354, fig. 169-172.

A discussion of habitat relations, etiology, and control of the fungus.

Brack Rot, Lear Spot, AND CANKER OF PomAcEousS FRUITS 133

Edgerton, C. W.
1908 Two little-known Myxosporiums. Ann. myc. 6:48-53, fig. 1-
Points out similarity and difference between the cankers caused by Sphaeropsis ee

and a new species of Myxosporium, called M. corticolum. The synonymy of S.
Malorum is given.

Ellis, J. B.
1880 On the variability of Sphaeria Quercuum Schw. Philadelphia
Acad. Nat. Sci. Proc. 1879:66—70.

Author would include several enumerated species of Sphaeria, Botryosphaeria, Dothidea,
and Melogramma under one species, and the name Melogramma fuliginosa is accepted.
Ascigerous forms accompanied by stylospore forms of the Diplodia or Sphaeropsis

type.

Ellis, J. B., and Everhart, B. M.
1892 The North American Pyrenomycetes, p. 1-793, pl. 1-

Eustace, H. J.
1908 Investigations on some fruit diseases. New York (Geneva) Agr.
Exp. Sta. Bul. 297:29-48, pl. 1-7.
Shows by experiment. that the fungus (Sphaeropsis Malorum) is not destroyed but its

growth is retarded in storage at temperatures ranging from 209° to 32°F. Gives results
of sulfur fumigation in storage.

Evans, I. B. P.
I910 The New York apple tree canker or black rot fungus in South
Africa. Transvaal agr. journ. 7:62—-64, pl. 7.

Calls attention of South African growers to the presence of ‘‘another imported fungus,
and one which it will not be well to neglect.”

Faurot, F. W.
1903. Black rot. Jn Report of fungous diseases occurring on cultivated
fruits during the season of 1902. Missouri State Fruit Exp.
Sta. Bul. 6:6-7.

The name blossom rot is employed for calyx-end infections on apples. Symptoms are
described.

t9g12 Black rot. Jn Common orchard troubles, spray mixtures, and
spray calendar. Missouri State Fruit Exp. Sta. Bul. 23:

14-15, fig. 8-0.
States that black rot, also called blossom-end rot, occurs largely on fruits of which the

skin has been broken, and that owing to the habits of the fungus it is not controlled
by spraying.

Floyd, Bayard F.
1905 Apple canker. Black rot. Jn Some common fungous diseases
and their treatment. Missouri State Hort. Soc. Ann. rept.
48: 432.

Notes that windfall apples are very susceptible.

Freeman, E. M.
1905 Black rot of apple (Sphaeropsis Malorum Peck). Jn Minnesota
plant diseases, p. 363-364, fig. 194.

Gives a short general account of black rot, leaf spot, and canker.

134 BULLETIN 379

Fiickel, L. a

1869 Symbolae mycologicae, p. 1-459, pl. 1-6.

Desens of Diplodia pseudodiplodia Fckl. (p. 393) and Diplodia Malorum Fckl.
Pp. 395).

Galloway, B. T.

1892 Report on the experiments made in 1891 in the treatment of
plant diseases. U.S. Agr. Dept., Veg. Path. Div. Bul. 3:1—-
76. Illustrated.

Gives (p. 39) an account of petal and young fruit infection induced by Sphaeropsis
Malorum.

Garman, H.
1895 Spraying experiments in 1895. Kentucky Agr. Exp. Sta. Bul.
59:111-129. Illustrated.

Sphaeropsis Malorum said (p. 127) to be the cause of most of the fruit rot in the State.

1908 Brown rot of apples. Jn 1. Spraying apple trees. 2. Apple
orchard pests in Kentucky. Kentucky Agr. Exp. Sta. Bul.
TABOOS OO:

The disease on apple fruit (due to Sphaeropsis Malorum) is called brown rot, and spray-
ing experiments for the control of the disease are reported.

Giddings, N. J.
1908 Apple canker. Jn The occurrence of plant diseases in 1907.
Vermont Agr. Exp. Sta. Ann. rept. 20:331.
Apple canker, caused by Sphaeropsis Malorum, said to be rather prevalent in some

orchards. _ The statement is made that the disease is easily controlled by pruning
and spraying, and is thus kept down in most well-tended orchards.

Green, W. J., Selby, A. D., and Gossard, H. A.

1915 Spraying program for orchards with combinations recommended.
Ohio Agr. Exp. Sta. Cire. 149:53-60.

Suggest (p. 54-55) a combination of insecticide and fungicide for control of codling
moth, apple scab, and black rot.

Griffon, E., and Maublanc, A.

1g10 Sur des espéces de Sphaeropsis et de Diplodia parasites du
poirier et du pommier. Soc. Myc. France. Bul. 26:307-316.
Illustrated.

Discuss symptoms, and several species of fungi on apple and pear. The conclusion
is reached that .these trees may be attacked by Sphaeropsis and Diplodia, which act
as wound parasites. The species involved are regarded as distinct and are briefly

described; these are Sphaeropsis Malorum Peck, Sphaeropsis pseudodiplodia (Fckl.)
Del., and an undetermined Diplodia.

Gussow, H. T.
1911 Black rot (Sphaeropsis Malorum Peck.). Im Report of the
Dominion Botanist. Experimental Farms (Canada). Rept.
IQII: 246-247.

Discusses symptoms and control.

Brack Rot, Lear Spot, AND CANKER OF PoMACEOUS FRUITS 135

Halsted, B. D.

1892 The black rot of the quince. J Some fungous diseases of the
quince fruit. New Jersey Agr. Coll. Exp. Sta. Bul. 91:8-10,
fig. 5-6.

Concludes from observation and experiment that the species of Sphaeropsis on quince,
apple, and pear are the same. States that the fungus causes one of the most destruc-
tive decays of the quince, and that the spores pass through the air or are carried by
insects.

1894 Decays of mature apples. Jn Report of the Botanist. New
Jersey Agr. Exp. Sta. Ann. rept. 14: 367-377, fig. 35-41.

Symptoms of black rot well described (p. 374-375). Author makes the point that the
fungus probably gains access through aoa of the flower at the free end.

Harrison, Charles
1823 A treatise on the culture and management of fruit trees, p. 1-356.
Illustrated.

Attributes (p. 341-343) canker to such causes as injudicious pruning, bruising, nailing,
bad subsoil. Surgical methods recommended.

Hartig, R.

1894 Text-book of the diseases of trees, p. 1-331. (Translated by Somer-
ville and Ward.)

Hartley, C. P.

1908 a Some apple leaf-spot fungi. Science n. s. 27: 212.
Eeporel the finding of eighteen different species of fungi on apple leaf spots in West
irginia, Sphaeropsis Malorum being among the common ones.
1908b Some apple leaf-spot fungi. Science n. s. 28:157—-159.

Gives brief historical review of the question of the etiology of apple leaf spot. A list
of several species of fungi found on spotted leaves is given, and inoculation experi-
ments with certain of these are reported. Results indicate that Coniothyrium pirina
is a wound parasite, while Coryneum foliicolum appeared to be even less parasitic.

1913 Twig canker on black birch. Phytopath. 3: 248-249.

Reports the isolation of a Sphaeropsis, closely resembling S. Malorum but with
somewhat smaller spores, from swollen cankered black birch twigs (Betula lenta L.).
Inoculation experiments show that the organism is parasitic only under certain
conditions, nor is it regarded as the cause of the swollen cankers.

Heald, F. D.

1906 The black-rot 0 apples due to Sclerotinia fructigena. Nebraska
Agr. Exp. Sta. Ann. rept. 19:82-91. Illustrated. (See also

p22, 61-)
Points out that the term black rot is a confused one, having been used for diseases caused

by both Monilia and Sphaeropsis. The two diseases are compared and contrasted
as to symptoms.

Hedges, Florence, and Tenny, L. S.

1912 A knot of citrus trees caused by Sphaeropsis tumefaciens. U. 5S.
Plant Indus. Bur. Bul. 247:1-74.. Illustrated.

Hesler, L. R.
1912 The New York apple tree canker. Indiana Acad. Sci. Proc.
IQII: 325-339, fig. 1-7.

Gives data concerning the geographical distribution, importance, symptoms, etiology,
and control of the disease. The synonymy of the fungus is reviewed.

136 BULLETIN 379

1913 Physalospora Cydoniae. Phytopath. 3: 290-295. Illustrated.

Proves experimentally the genetic connection between Physalospora Cydoniae and Sphae-
ropsis Malorum.

1914 Biological strains of Sphaeropsis Malorum. Phytopath. 4:45.

Results of cross-inoculation work with the fungus from several host plants indicate that
there is one large morphological species embracing many biological races.

Hewitt, J. L., and Hayhurst, P.
1911 Diseases of apple trees and fruit caused by fungi and insects.
Arkansas Agr. Exp. Sta. Bul. 109: 409-445.

Note the occurrence of black rot and leaf spot in Arkansas (p. 438, 440-441).

Howitt, I. E.
1913. Fungus diseases. Ontario Agr. Coll. and Exp. Farm. Ann.
rept. 38: 29-30.

Notes the occurrence of black rot canker along with other plant diseases.

Ingram, Della
1912 Preliminary notes on a twig blight of Quercus prinus. Phyto-
path. 2: 96-97.

Mentions an apparently serious disease of the chestnut oak which occurs in Connecticut,
Virginia, Maryland, and Pennsylvania. The organism associated with the disease is
said to agree with Dothiorella quercina (C. & Ell.). (Cf. Rankin, W. H., 1914, p. 141.)

Jehle, R. A.

1913. The brown rot canker of the peach. Phytopath. 3: 105-110,
(Dl, Mey tes Th

Reports successful use of coal tar on wounds of peaches.

Jones, L. R., and Giddings, N. J.
1907 Apple canker. In The occurrence of plant diseases in Vermont
in 1906. Vermont Agr. Exp. Sta. Ann. rept. 19: 231-232.

The fungus Sphaeropsis Malorum said to continue its destructive invasion and to be the
cause of every case of apple canker examined.

Kern, F. D.

1906 Indiana plant diseases in 1905. Purdue Univ. Agr. Exp. Sta.
Bul) mrrsr2n—r3a.
Black rot of the apple, pear, and quince reported (p. 125) from the southern part of the
State only.
1907 Indiana plant diseases in 1906. Purdue Univ. Agr. Exp. Sta.
Bul. 119:425-436.

Mentions (p. 428) black rot and canker of the apple, and black rot of quince, present
to some extent in the southern part of the State.

Kinney, L. F.

1895 a Some special orchard treatment of the apple, pear, and quince.
Rhode Island Agr. Exp. Sta. Bul. 31:1-17, fig. 1-9.

Reports (p. 10) fails to control black rot of quince by spraying.

1895 b The leaf spot of the apple and pear. J Horticultural Division.
Rhode Island Agr. Exp. Sta. Ann. rept. 7: 188-189, fig. 7-8.

Points out resemblance of injury by apple leaf miner (Tischeria malifoliella Clemens)
to apple leaf spot. Spots on the leaves, and spores of Phyllosticta pirina, which
is regarded as the cause, are figured.

Brack Rot, Lear Spot, AND CANKER OF PoMACEOUS FRUITS 137

1895c The brown rot. Jn Horticultural Division. Rhode Island
Agr. Exp. Sta. Ann. rept. 7:192—-193, fig. 12.

Symptoms are given. The disease on the fruit (which author calls brown rot)
and spores of the fungus are figured.

Kirchner, Oskar
1906 Die Krankheiten und Beschadigungen unserer landwirtschaft-
lichen Kulturpflanzen, p. 1-647.

States (p. 440) that the canker disease of apple trees, caused by Diplodia pseudodiplodia
‘Thum., occurs in North America, France, and perhaps Germany.

Lamson, H. H.

1897 Department of Bacteriology. In Ninth annual report. New
Hampshire Coll. Agr. Exp. Sta. Bul. 48: 146-147.
Bordeaux mixture said to have had little effect in controlling leaf spot due to Phyllosticta
pirina; hence work was directed toward its control.
1899 Apple diseases. Jn Notes on apple and potato diseases. New
Hampshire Coll. Agr. Exp. Sta. Bul. 65: 106-107, fig. 38-39.
Notes the serious nature of leaf spot, which is said to be caused partly at least by
Phyllosticla pirina.
Igor Apple tree canker. Jn Thirteenth annual report. New Hamp-
shire Coll. Agr. Exp. Sta. Bul. 87: 130.

Reports the presence of a canker which is believed to be caused by a fungus.

1902 The cold storage of apples.— Part II. Influence of cold storage
on the decay of apples. Effect of wrapping apples in paper.
New Hampshire Coll. Agr. Exp. Sta. Bul. 93:75-81, fig. 1.

Sphaeropsis Malorum listed (p. 75) as one of three fungi which cause most of the rotting.
Author concludes (p. 81) that a temperature of 34° F. is more effective than 40° to
45° F., and that wrapping the fruit is of decided advantage in extending the keeping
period beyond the first of June. Clean newspaper said (p. 81) to be just as effective
as more expensive paper.

1903. Leaf spot. In Fungous diseases and spraying. New Hampshire
Coll. Agr. Exp. Sta. Bul. 1ro1:61-62. Illustrated.

Bordeaux mixture said to have little effect in controlling leaf spot of apple.

Lewis, C. E.
1909 Apple diseases caused by Coryneum foliicolum and Phoma
Mali. Maine Agr. Exp. Sta. Bul. 170:183-200, fig. 17-42.

Reports successful infection experiments with Sphaeropsis Malorum Peck on injured bark
and on uninjured apple leaves.

1912 Inoculation experiments with fungi associated with apple leaf
spot and canker. Phytopath. 2:49-62.

An account of experiments directed toward the determination of the parasitism of
such fungi as Sphaeropsis Malorum, Phyllosticta limitata Peck, Coniothyrium pirina
(Sacc.) Sheldon, and Coryneum foliicolum Fckl. Author concludes that a part of
the leaf spot in Maine is due to Sphaeropsis Malorum, but that a similar spotting
is due to bordeaux mixture; that Sphaeropsis Malorum is the only fungus isolated
from apple leaves in the State which causes spots when inoculations are made from
pure cultures; and that, of the several fungi studied, this fungus does the greatest
damage to branches and to twigs.

Lewis, I. M.
1908 Apple leaf spot. New Hampshire Agr. Exp. Sta. Ann. rept.
19-20: 365-369, pl. 8-9.

Gives a historical review of the causal nature of the disease, and presents inoculation
and control data.

138 BULLETIN 379

Lochhead, William
1905 Black rot canker. Ontario Agr. Coll. and Exp. Farm. Ann.
rept. 30:49, fig. 4-5.
Defines the term canker and outlines control measures.
1909 Apple diseases. Jn Fungous diseases in Quebec in 1908. Quebec
Soc. Prot. Plants from Ins. and Fung. Dis. Ann. rept. 1:31.

The prevalence of the canker form of this disease is noted.

Longyear, B. O.
1904 Fungous diseases of fruits in Michigan. Michigan State Agr.
Coll. Exp. Sta. Spec. bul. 25:1—-68, fig. 1-42.

Records the black rot disease of apple (p. 10-13), pear (p. 16), and quince (p. 20).

Lunge, George
1909 Coal tar and ammonia, Part I, chap. 1, p. 1-15.

Notes differences in tars, both physical and chemical, depending on the origin. Tar
obtained from the same material also differs yery much in composition, according to
the temperature of the dry distillation, and even according to the shape of the retorts.

McAlpine, D.
1902 Fungus diseases of stone-fruit trees in Australia and their treat-
ment, p. 1-165. Illustrated.
Lists (p. 133, 134) Diplodia Malorum on peach and plum twigs.

M’Cormack, Edna F.
1g10 Black rot of the apple. In Fungous diseases of the apple.
Indiana State Entomologist. Rept. 3:142-144. Illustrated.

Symptoms discussed.

McCready, S. B.
1910 Black rot canker (Sphaeropsis Malorum Peck). Ontario Agr.
Coll. and Exp. Farm. Ann. rept. 35:41—-42.

Brief reference to hosts, distribution, etiology, and control.

Ig1r_ Black rot of apple. Ontario Agr. Coll. and Exp. Farm. Ann.
rept. 36:37.
Reports use of lead paint and gas tar as wound dressings; the latter found to give
better protection.

Mangin, L.
1901 Sur une nouvelle maladie des pommiers causée par le ‘ Diplodia
pseudo-diplodia.” Journ. agr. prat. n. s. 2:138-139.

Reports occurrence of the disease on apple branches in France, and gives suggestions
for control.

Morse, W. J.
1909 Notes on plant diseases, 1908. Maine Agr. Exp. Sta. Bul.
164:1-28. Illustrated.

States (p. 3-4) that Sphaeropsis Malorum from leaf spot produced decay of fruit as a
result of artificial inoculation. States (p. 10) that self-boiled lime-sulfur seemed
effective in controlling leaf spot.

Brack Ror, Lear Spot, AND CANKER OF PomAcEous FRUITS 139

Morse, W. J., and Lewis, C. E.
1910 Maine apple diseases. Maine Agr. Exp. Sta. Bul. 185:335-302.
Illustrated.

Notes on the etiology of leaf spot and canker. Canker fungus in Maine orchards follows
frost injury.

Munson, W. M.
1909 Apple enemies, and how to fight them. West Virginia Univ.
Agr. Exp. Sta. Bul. r21r:353-366.

Control measures for leaf spot and canker given (p. 360-362).

Norton, J. B. S., and Symons, T. B.
1907 Black-rot (Sphaeropsis Malorum). In Control of insect pests and
diseases of Maryland crops. Maryland Agr. Exp. Sta. Bul.
115:178.

Give brief recommendations for the control of black rot, leaf spot, and canker.

O’Gara, P. J.
1902 Notes on canker and black-rot. Science n. s. 16: 434-435.

Notes a case of girdling of branches of sumac (Rhus glabra L.) by Sphaeropsis rhoina
(Schw.) Starb., which fungus, after careful cultural and inoculation experiments, is
regarded as probably identical with Sphaeropsis Malorum.

Orton, C. R.
1914 Black rot. In Some orchard diseases and their treatment.
Pennsylvania State Hort. Assoc. Proc. 55: 43-56. Illustrated.

Author states that Sphaeropsis Malorum rarely if ever produces cankers on its own
initiative. He notes its wide occurrence on various plants, and says that a perfect
stage has recently been found on apple, quince, oak, grape, witch-hazel, and other
hosts.

Orton, W. A.
1902-1907 Plant diseases in the United States in rgo1-1907. U. S.
Agr. Dept. Yearbook 1901:669; 1902:715; 1903:550;
1904:582-583; 1905:603-604; 1906: 499-500; 1907: 577—
579.

Gives notes on the occurrence and destructiveness of black rot, leaf spot,
and canker of apple, pear, and quince.

Paddock, Wendell
1898 a An apple canker. Science n. s. 8:595~-596.

Reports preliminary experiments in canker investigation. Cultures of fungi from
cankers showed Schizophyllum commune, and a dark-spored fungus which is said
to resemble Sphaeropsis Malorum Peck.

1898 b Additional notes on an apple canker. Science n. s. 8:836—-837.

Suggests that Sphaeropsis Malorum Peck is parasitic on the wood of pear and quince
as well as on that-of apple. Cross-inoculations of the fruits of these three plants

gave positive results.

1899 a An apple canker. Western New York Hort. Soc. Proc. 44:
58-63. Illustrated.
(See 1899 b, of which this is a popular presentation.)
1899 b The New York apple-tree canker. et York (Geneva)
Agr. Exp. Sta. Bul. 163:177-206, pl. 1
Contains an account of host relationships, names of the disease, symptoms, etiology,

and control. Presents conclusive data proving that Sphaeropsis Malorum is
the cause of canker on apple; considerable data indicate that this species of

Sphaeropsis also occurs on many other plants.

140 BULLETIN 379

1900 The New York apple-tree canker (Second report). New York
(Geneva) Agr. Exp. Sta. Bul. 185: 203-213, pl. 1-4.

States that Sphaeropsis Malorum occurs on apple, pear, and quince fruits, and on apple,
pear, and hawthorn trees; and that it probably occurs on several other plants, but
experiments are not regarded as warranting this as a definite conclusion. Notes that
apple leaves are occasionally attacked by a Sphaeropsis.

Parkinson, John

1629 Paradisi in sole paradisus terrestris, p. 1-612. Illustrated.
Briefly outlines (p. 550) the nature and control of canker. Of historical importance.

Parrot, P. J., and Fulton, B. B.
1913 Notesontreecrickets. Journ. econ. ent.6:177—180. Iilustrated.

Note that the penetration of apple bark tissues by the ovipositor of the tree cricket
is apparently attended by an infection of some unknown fungus or bacterium, which
results in the formation of a canker indistinguishable in its appearance and effects
from the New York apple tree canker or the fire blight canker.

1914 Tree crickets injurious to orchard and garden fruits. New York
(Geneva) Agr. Exp. Sta. Bul. 388:415-461. Illustrated.

Authors note (p. 442) that injuries by tree crickets are followed by some infectious agent,
and that these lesions, in their external appearances and their effects, resemble super-
ficially certain stages of the New York apple tree canker caused by Sphaeropsis
Malorum.

Peck, C. H. :
1879 Report of the Botanist. New York State Mus. Nat. Hist.
Ann. rept. 31: 19-60.

ee (p. 20-21) the discovery of Sphaeropsis Malorum on apple fruits in Schoharie
ounty.

1881 Report of the Botanist. New York State Mus. Nat. Hist.
Ann. rept. 34: 24-58, pl. 1-4.
Describes (p. 36) symptoms of black rot, and points out the fact that the distinction

between Sphaeropsis and Diplodia sometimes fails, since both one- and two-celled
spores are found in the same spore case.

Pollock, J. B., and Kauffman, C. H.
1905 Michigan fungi. Michigan Acad. Sci. Rept. 7: 57-67.
List Sphaeropsis Mali (West.) Sacc. and S. Malorum Peck.

Potebnia, A.
1907. Mycologische Studien. Ann. myc. 5: 1-28, pl. 1-3, fig. 1-43.

Discusses mycelial development, including spore germination and protoplasmic
streaming.

1910 Beitrage zur Micromycetenflora Mittel-Ruszlands. Ann. mye.
8: 42-93, fig. 1-38.
States that the pycnidia of S. pseudodiplodia (Fckl.) Del. arise meristogenetically.
1912 Pilzliche Symbionten. 2. Sphaeropsis und Helicomyces, p. 28.
Illustrated. (Separate sent by Potebnia to the writer.)

Price, H. L.
1909 Black rot. Jn Fighting the insect pests and diseases of orchard,
field, and garden crops. Virginia Agr. Exp. Sta. Circ.
7>TO-21, fig. 2

Recommendations for the control of black rot, leaf spot, and canker.

Brack Ror, Lear Spot, AND CANKER oF Pomaceous Fruirs 141

Quaintance, A. L., and Scott, W. M.
1912 Apple leaf-spot. Ju The more important insect and fungous
enemies of the fruit and foliage of the apple. U. S. Agr.
Dept. Farmers’ bul. 492:35-36, fig. 20.

Discuss the importance, symptoms, etiology, and control of apple leaf spot caused by
Sphaeropsis Malorum.

Rankin, W. H.
1914 Sphaeropsis canker of Quercus prinus. Phytopath. 4: 44-45.

Reports Sphaeropsis Malorum Berk. as causing twig and limb cankers on chestnut oak
(Quercus prinus L.), the account being based on observation and inoculation experi-
ments. Regards the disease as the one described by Miss Della Ingram in
Phytopathology 2:96 (p. 136).

Reddick, Donald
1912 Frost injury. New York State Fruit Growers’ Assoc. Proc.
II: 34-41, fig. 1-2.

Sphaeropsis Malorum said to be usually found following frost injury.

Reed, H. S.
1908 Fall blossoming of the apple induced by the black rot. Plant

world 11: 256-257

Notes a case in Bee inseecews Malorum inhibited the normal activities of an apple
tree, allowing the tissues to carry on the growth which would normally have been
deferred for several months, and resulting in the unfolding of normal blossoms on
October 5.

Reed, H. S., and Cooley, J. S.
1911 Black rot (Sphaeropsis Malorum). Jn Plant diseases in Virginia
in the years 1909 and 1910. Virginia (Polytech. Inst.) Agr.
Exp. Sta. Ann. rept. 1909-1910: 102-103, fig. 21.

Record black rot, leaf spot, and canker. Report pycnospores discharging from pycnidia
on leaves at Blacksburg on June 25, I910.

Reed, H. S., Cooley, J. S., and Rogers, J. T.
1912 Foliage diseases of the apple. Virginia (Polytech. Inst.) Agr.
Expy tae bul Toss 1—24, ties T—13)

Give points concerning the varietal susceptibility of apples; the distribution, importance,
and symptoms of the disease; and the life history of the fungus.

Reed, H. S., and Crabill, C. H.
1913 Black rot (Sphaeropsis Malorum). Jn Plant diseases in Virginia
in the years 1911 and 1912. Virginia (Polytech. Inst.) Agr.
Exp. Sta. Ann. rept. 1911-1912: 36, fig. 3.

Note that Sphaeropsis Malorum occurs on twigs previously killed by the fire blight
organism. Figure a multilocular sterile (?) pycnidium.

Reed, H. S., and Stahl, H. S.

191m The erepsins of Glomerella rufomaculans and Sphaeropsis

Malorum. Journ. biol. chem. 10: 1rog-112.
Authors find evidence of erepsin produced in pure cultures.

Roberts, J. W.
1913 The “rough-bark”’ disease of the Yellow Newtown app’e.
U.S. Plant Indus. Bur. Bul. 280:1—-15, pl. 1-3.

Reports (p. 9, 15) Phomopsis Mali, a new species, associated with Sphaeropsts Malorum
on leaf spots.

142 . BULLETIN 379

1914 Experiments with te leaf-spot fungi. Journ. agr. research
2: 57-66, pl. 7, fig. 1

Reports the isolation of ee species, including Sphaeropsis Malorum, from apple leof
spots. A new species, Alternaria Mali, is in the list and is technically described.
From experiments conducted it is concluded that this species may be classed asa
rather strong facultative parasite.

Rose, D. H.

1914 Ring rot. Also, Black rot (Sphaeropsis Malorum). Jn Biennial
report. Missouri State Fruit Exp. Sta. Bul. 24 (Bienn. rept.
IQ13—1914): 20, 23-24, pl. 5, fig. 1-2.

Ring rot, or blossom-end rot, of the apple fruit thought to be due to frost injury at

blossoming time, followed by Sphaeropsis Malorum Peck. Author gives notes on the
destructiveness of black rot.

Ruggles, A. G., and Stakman, E. C.
1g1r_ Black rot Jn Orchard and garden spraying. Minnesota Univ.
Act Hxpy stae eBule) comes.

Symptoms of black rot given.

Saccardo, P. A.
1884a Phoma Malorum (Berk.) Sacc. Syll. Fung. 3: 152-153.

A technical Latin description is given. Author lists Sphaeropsis Malorum Berk. in
synonymy.

1884 b Sphaeropsis Malorum Peck. Syll. Fung. 3: 294.

Describes the fungus which Peck (1881) reports and regards as new, thus giving
rise to the name Sphaeropsis Malorum Peck.

Salmon, E. S.
1907 Apple leaf-spots. Gard. chron. ser. 3:42:305-306, fig. 120-124.
A brief discussion of varietal susceptibility and etiology of leaf spots caused by a species

of Phyllosticta and one of Sphaeropsis. The author is in doubt as to whether the
latter species is S. Malorum.

Scott, W. M.
1906 The control of apple bitter-rot. U.S. Plant Indus. Bur. Bul.
Ope HAO, jolly i,
Gives (p. 27-33) results of experiments for the control of leaf spot in connection with
apple scab, sooty blotch, and bitter rot.

1908 Apple leaf-spot. Jn Self-boiled lime-sulphur mixture as a

promising fungicide. U.S. Plant Indus. Bur. Cire. 1:12.
States that it appears that leaf spot may be prevented by this fungicide, but no data
are cited.
1912 Apple leaf-spot, or frog-eye. In Spraying to control the important
insects and fungous diseases affecting the fruit and foliage of
the apple. Thomsen Chemical Co. (Baltimore, Md.). Cire.

Mea, jolly 2, 18h, a

Scott, W. M., and Quaintance, A. L.
1907 Leaf-spot diseases. Im Spraying for apple diseases and the
codling moth in the Ozarks. U.S. Agr. Dept. Farmers’ bul.
283:18-20, fig. 3

Authors give recommendations for the control of leaf spot, which, as they state, may
be due to Sphaeropsis Malorum.

Brack Rot, Lear Spot, AND CANKER oF Pomaceous Fruits 143

Scott, W. M., and Rorer, J. B.

1908 Apple leaf-spot caused by Sphaeropsis Malorum. U. S. Plant
Indus. Bur. Bul. 121:45~54, pl. 3-4.

Authors discuss the common names of the leaf spot, its history, geographical occur-
rence, Importance, symptoms, etiology, and control. Proof of the pathogenicity of
Sphaeropsis Malorum on apple leaves is given, together with a study of the réle of
associated fungi on leaf spots.

1909 Apple blotch, a serious disease of Southern orchards. U. S.
Plant Indus. Bur. Bul. 144:1-28, pl. 1-6.

Authors suggest (p. 11) that Sphaeropsis Malorum is a factor in the killing of apple buds
Further investigation is deemed desirable.

Scribner, F. L.

1890 Black-rot of the apple. Fungus diseases of the grape and other
plants and their treatment, p. 81-83, fig. 1606.

Descriptions of the disease and of the fungus, called Macrophoma Malorum, are given.

Seaver, F. J.
1908 Color variation in some of the fungi. Bul. Torrey Bot. Club
35: 307-314.

Points out that color characters are misleading and misused in the Hypocreales.

Selby, A. D.
1g00 A condensed handbook of the diseases of cultivated plants in
Ohio. Ohio Agr. Exp. Sta. Bul. 121:1-69, fig. 1-54.

Notes (p. 14) the disease on the leaves and fruit of apple and quince.

tg10_ Black-rot. Jn A brief handbook of the diseases of cultivated
plants in Ohio. Ohio Agr. Exp. Sta. Bul. 214:368-360,
436, fig. 1-105.
Notes the importance of the disease in Ohio.
1913 Disease susceptibility of apple varieties in Ohio. Ohio Agr. Exp.
Sta. (Cire: 133:'53—56:

Indicates degree of susceptibility of apple varieties to black rot and canker.

Shear, C. L.
1910 Life history of Melanops Quercuum (Schw.) Rehm forma Vitis

Sace. Science n. s. 31: 748.
Pure cultures of ascospores af Melanops Quercuum (Schw.) Rehm forma Vitis Sacc.
[= Botryosphaeria Berengeriana de Not. = B. fuliginosa (M. & N.) E. & E.] said to
produce a pycnidial form which agrees with Sphaeropsis Malorum Berk. and Diplodia
pseudodiplodia Fckl.
1913 Some observations on phytopathological problems in Europe and
America. Phytopath. 3: 77-87.
Sphaeropsis Malorum reported (p. 81-82) as doing no noticeable injury in orchards
from Italy to England.
1914 Life history of Sphaeropsis Malorum Berk. Phytopath. 4: 48-49.
Concludes from cultural studies the ascosporic form of Sphaeropsis Malorum Berk.
is Melanops Quercuum f. Vitis.

Shear, C. L., and Wood, Anna K.

1913 Studies of fungous parasites belonging to the genus Glomerella.
U.S. Plant Indus. Bur. Bul. 252:1-110. LIllustrated.

Discuss host relationships, variability, and parasitism of Glomerella.

144 BULLETIN 379

Sheldon, J. L. :

1905 A report on plant diseases of the State. West Virginia Univ.
Agr. Exp. Sta. Bul. 96:69-99. Illustrated.
Black rot (p. 74), leaf spot (p. 74-75), and canker (p. 74) reported.

1907. The taxonomy of a leaf-spot fungus of the apple and other
fruit-trees. Torreya 7: 142-143.
The name of the leaf spot, or frog-eye, organism is changed from Phyllosticta pirina Sacc.
to Coniothyrium pirina (Sacc.) Sheldon.
1908 Another leaf-spot fungus of the apple. Torreya 8: 139-141.

Illosporium malifoliovum n. sp. is said to be concerned with the leaf spot, in a secondary
manner. This fungus is described.

Smith, R. I., and Stevens, F. L.

1910 Leaf spot. Also, Black rot. In Insects and fungous diseases of
apple and pear. North Carolina Agr. Exp. Sta. Bul. 206:
94, 95, 102-103, fig. 23.

Call the disease Sphaeropsose, and state that perhaps one, but probably several, species
are responsible for leaf spot.

Stene, A. E.

1910 Some suggestions for Rhode Island apple growers. Rhode
Island State Agr. Bd. Ann. rept. 25:93-181. Illustrated.

Leaf spots and canker said to be general in the State (p. 152-153).

Stevens, F. L., and Hall, J. G.

1907 Sphaeropsis on apple twigs. In Some apple diseases. North
Carolina Agr. Exp. Sta. Bul. 196: 52-53.

1909 a Notes on plant diseases occurring in North Carolina. North
Carolina Agr. Exp. Sta. Ann. rept. 31: 66-82, fig. 1-10.
Black rot and canker reported (p. 66). Sphaeropsis and an ascomycetous fungus
found; name of latter not given. Sphaeropsis reported (p. 75) as a canker-pro-
ducing fungus on pear.
1909b Variation of fungi due to environment. Bot. gaz. 48: 1-30,
fig. 1-37. See also North Carolina Agr. Exp. Sta. Ann.
rept. 32 (1908-1909): 47-71, fig. 1-37.

Authors discuss observations on the influence of environment on the characters of
certain fungi.

Stevens, F. L., and Sherman, F.
1903. The black rot. Also, The black rot of the quince. In Insect
and fungus enemies of the apple, pear, and quince, with methods
of treatment. North Carolina Agr. Exp. Sta. Bul. 183:72,
Sppaile, WA.

Symptoms and control measures of black rot and canker given.

Stewart, F. C.
1896 A new leaf-spot disease of apples. Jn Report of the Mycologist.
New York (Geneva) Agr. Exp. Sta. Ann. rept. 14 (1895):
545-546.

Records Phyllosticta limitata n. sp. on apple leaves on Long Island. Technical descrip-
tion given.

Brack Rot, LEAF Spot, AND CANKER OF PoMAcEousS FRuITS 145

1904 Apple canker. Jn Fungi and fungous diseases. Western New
York Hort. Soe. Proc. 49: 53.

States that spraying for apple canker caused by Sphaeropsis Malorum is only a partial
preventive; a matter not understood.

1909 Apple leaf spot. Jn Recent investigations on plant diseases.
Western New York Hort. Soc. Proc. 54: 78-79.

Believes that the leaf spot problem in New York is not completely solved. Points out
that spraying often fails to control.

1910 Notes on New York plant diseases, I. New York (Geneva) Agr.
Exp. Sta. Bul. 328:303-404, pl. 1-18.

Discusses (p. 312-313) occurrence of leaf spot in New York. Gives (p. 323-324) an
account of a peculiar disease of the trunk of Walbridge apples and suggests that
Sphaeropsis Malorum may have been a factor in producing the same. Suspects (p. 377-
379) that the fungus also causes the failure of grafts of the pear.

Stewart, F. C., and Blodgett, F. H.
1899 A fruit-disease survey of the Hudson Valley in 1899. New York
(Geneva) Agr. Exp. Sta. Bul. 167:273-308, pl. 1-4.

Notes on the geographical occurrence of the leaf spot and canker in the Hudson Valley
(p. 283, 284, 301-302).

Stewart, F. C., and Eustace, H. J.
1902. Two unusual troubles of apple foliage. New York (Geneva)
Acre Exp. sta.) (ull 220v205—233) pl, 15.

Authors conclude that spray material caused spotting of apple foliage; suspect the
parasitism of Phyllosticta; suggest that drops of rain may act as lenses and concen-
trate the sun’s rays, overheating the tissue beneath.

Stewart, F. C., Rolfs, F. M., and Hall, F. H.

1g00_ A fruit-disease survey of western New York in 1900. New York
(Geneva) Agr. Exp. Sta. Bul. 191: 289-331, pl. 1-6.

Note geographical occurrence of the disease in western New York.

Stone, G. E.
1914 Lime and sulfur solutions. Massachusetts Agr. Exp. Sta.
Cires soni.

Lime and sulfur said to hold leaf spot in check, and believed to have material effect on
cankers.

Stone, G. E., and Fernald, H. T.

1908 Canker. In Fungicides, insecticides, and spraying directions.
Massachusetts Agr. Exp. Sta. Bul. 123:16.

Suggestions for canker control are given.

Stone, G. E., and Monahan, N. F.
1907 The lime and sulfur mixture as a fungicide. In Report of the
Botanist. Massachusetts (Hatch) Agr. Exp. Sta. Ann. rept.
19: 167.

State that observations seem to indicate that spraying with lime and sulfur succeeds to
some-extent in controlling canker.

Stone, G. E., and Smith, R. E.
1903 Apple-leaf spot. Jn Report of the Botanists. Massachusetts
(Hatch) Agr. Exp. Sta. Ann. rept. 15:27, 32-34.

Frost followed by cold wet weather caused apple leaf spot.

146 BULLETIN 379

Sturgis, W. C.
1893 a Black-rot (Sphaeropsis Malorum Peck). J Common fungous
diseases and their treatment. Connecticut (New Haven)
Agr Exp. Sta; Bul) 1156-7.
Black rot of apple, quince, and pear noted.
1893 b Black rot of quinces. Jn Report of the Mycologist. Con-
necticut (New Haven) Agr. Exp. Sta. Ann. rept. 1892: 43-44.
Description of black rot disease of quince fruits.
1894 Black rot (Sphaeropsis Malorum Peck). Jn Report of the
Mycologist. Connecticut (New Haven) Agr. Exp. Sta.
Ann. rept. 17: 78-79.

Reports inoculation and spore germination data. States that the wind and other
agencies carry the fungus spores.

Taft, L. R., and Davis, G. C.

1895 Black rot (Sphaeropsis Malorum Berk.). In The pests of the
orchard and garden. Michigan State Agr. Coll. Exp. Sta.
Bulk ronan.

Briefly describe black rot and give suggestions for control.

Taubenhaus, J. J.

tg12 A further study of some Gloeosporiums and their relation to a
sweet pea disease. Phytopath. 2: 153-150, pl. 16, fig. 1-19.

States (p. 157) in a footnote that black rot was very prevalent in the very dry summer
of IQIT.

Taylor, W. A.
1914 Fruit diseases. In Report of the Chief of the Bureau of Plant
Industry. U.S. Agr. Dept. Rept. 1913: 105-133.

States (p. 107) that a variety of Melanops Quercuum has been shown to be the perfect
stage of Sphaeropsis Malorum.

Thumen, F. von
1879 Fungi pomicoli, p. ro8. (Cited from Baccarini, 1890.)

Waite, M. B.
1898a An apple canker. Western New York Hort. Soc. Proc.
43: 9-11.

Briefly outlines the history and distribution of the disease, and suggests that the
cause may be Schizophyllum commune. Control measures suggested.

1898b An apple canker. Rural New-Yorker 57: 82, fig. 32.
Essentially the same paper as the preceding.
1906 Fungicides and their use in preventing diseases of fruits. U. S.
Agr. Dept. Farmers’ bul. 243:1—32, fig. 1-17.
Brief notes (p. 19) on control of black rot, leaf spot, and canker.
1908 Apple leaf blight. Im Diseases of orchard trees and fruits.
Pennsylvania Agr. Dept. Ann. rept. 13: 450-452.
Gives treatment for leaf spot.
1910 Experiments on the apple with some new and little-known
fungicides. U.S. Plant Indus. Bur. Cire. 58:1-109.

Notes on leaf spot.

Brack Rot, Lear Spot, AND CANKER OF PomaAcEous FRUITS 147

Walker, Leva B.
1908 A new form of Sphaeropsis on apples. Nebraska Agr. Exp.
Sta. Ann. rept. 21: 34-44, fig. 1-10.
Compares typical Sphaeropsis Malorum with a new form, the latter having larger

spores, pycnidia with long necks, and no ostiole, and being more virulent in producing
black rot.

Wallace, Errett

1913 Scab disease of apples. Cornell Univ. Agr. Exp. Sta. Bul.
335:541-624. Illustrated.

Warren, G. F., and McCourt, W. E.
1905 The apple-tree canker. Jn An apple orchard survey of Wayne
County, New York. Cornell Univ. Agr. Exp. Sta. Bul.

226:341-345, fig. 86-87.

Attention is given to the economic importance of the canker and to control measures
followed by the growers in this section of the country. It is said that very few mature
Twenty Ounce trees are not badly cankered, and Esopus suffers seriously.

Whetzel, H. H.

1906 The blight canker of apple and pear trees. Western New York
Hort. Soc. Proc. 51: 36-45.

Compares fire-blight and New York apple-tree cankers.

1907 The New York apple tree canker. Jn Fighting the fungi in their
winter quarters. Cornell reading-course for farmers, March,
1907, p. 670-671, fig. 365.

Gives symptoms of canker and measures for its control.

Whetzel, H. H., and Stewart, F. C.
1908 New York apple-tree canker. In Insect pests and plant diseases.
V. _The control of plant diseases Cornell Univ. Agr. Exp.
Sta. Bull 252:355, fig. 165.

Suggestions for canker control are given.

Wilcox, E. M.
1905 Black rot. Also Canker. In Diseases of the apple, cherry,
peach, pear, and plum; with methods of treatment. Alabama
(Auburn) Agr. Exp. Sta. Bul. 132:89-93, pl. 2, fig. 6.

Notes on symptoms and control of black rot and canker.

Wilcox, E. M., and Stone, R. E.

1909 Black rot (Sphaeropsis Malorum). In Directions for the control
of Nebraska plant diseases. Nebraska Agr. Exp. Sta. Ann.
rept. 22:31.

Give schedule for control of canker and black rot.

Wilson, G. W.

1913. New York canker. In Notes on three limb diseases of apple.
North Carolina Agr. Exp. Sta. Ann. rept. 35:47-49, fig. 1.

Brief summary of history, distribution, importance, and symptoms of the disease.
Author states that the fungus may enter the bark under certain conditions, and that it
does not travel in the wood.

148 BULLETIN 379

Wolf, F. A.
1910 The prevalence of certain parasitic and saprophytic fungi in
orchards as determined by plate cultures. Plant world
13: 190-202.
By use of trap cultures the author concludes that at no time during the period in which

exposures were made (September to May) were viable spores of Sphaeropsis Malorum
present in the atmosphere of the orchard.

1913 Control of apple black-rot. Phytopath. 3: 288-280.
Suggests that apple mummies are a source of the inoculum. Reports that in the
South lime-sulfur alone is effective against the disease; bordeaux 4-4-50 also
satisfactory. A spraying schedule is given.