JULY 21, 1899. ] 
are those which enter into the most cordial re- 
lations with a large body of students.”’ 
In the June number of the Journal of the 
Boston Society of Medical Sciences Dr. James 
H. Wright has a paper on the application of 
color screens to photomicography, in which he 
shows that by a proper use of filtering light 
media the clearness and accuracy of photomi- 
crographs may be greatly enhanced. 
SOCIETIES AND ACADEMIES. 
GEOLOGICAL CONFERENCE AND STUDENTS’ CLUB 
OF HARVARD UNIVERSITY. 
Students’ Geological Club, May 2, 1899.—Mr. 
A. W. Grabau gave a résumé of the paleontol- 
ogy of the Boston basin. 
Geological Conference, May 9, 1889.—Under 
the title ‘Tertiary Granitic Intrusives of the 
Yellowstone Park,’ Dr. T. A. Jaggaer, Jr., re- 
viewed Mr. Arnold Hague’s paper on ‘The 
Tertiary Volcanoes of the Absaroka Range’ 
(SCIENCE, IX., pp. 425-442). 
Students’ Geological Club, May 16, 1899.—At 
a special meeting of the Club, Mr. L. LaForge 
exhibited his collection of Chemung fossils. 
Geological Conference, May 23, 1899.—Three 
papers were presented at this final meeting of 
the year. Mr. A. W. Grabau discussed ‘Some 
Modern Stratigraphic Problems’ froma paleon- 
tological point of view. He emphasized the 
importance in paleontological work of the 
division of marine organisms into Plankton, 
Nekton, Benthos, Meroplankton and Pseudo- 
plankton, and held that extensive deposits of 
planktonic organisms enclosed by beds of shal- 
low water origin indicate a period when the 
land stood at baselevel. Benthonic animals 
are important as facies fossils, and the ben- 
thonic mode of living exerts a great influ- 
ence in the development of local faunas. Re- 
population of a district by a benthonic fauna 
which has occupied it at an earlier date— 
through the medium of meroplanktonic larve, 
as demonstrated by Walther—was illustrated 
by examples drawn from the Hamilton of west- 
ern New York. Graptolites and Ammonoids, 
as pseudoplanktonic organisms, are important 
as index fossils. 
Among local or provincial faunas acceleration 
SCIENCE. 
89 
was considered to be one of the foremost means 
of differentiating species. Thus, the Fuside 
of the Paris basin appear to have developed in- 
dependently from those of the Hampshire basin 
of England. In each area acomplete, distinct, 
phylogenetic series has been discovered. These, 
although parallel, present specific differences 
throughout ; while certain individuals suggest 
occasional migrations of species from one basin 
to the other. 
In considering the operation of barriers upon 
migration the case of the genus Fulgur was 
cited. This gastropod has inhabited the At- 
lantic coast between Cape Cod and the Gulf of 
Mexico since Miocene time, its northward 
and southward migration being prevented by 
climatic causes, due largely to topographic con- 
ditions. That their young are not carried to 
other similarly characterized shores appears to 
be due to the fact that the veliger stage is passed 
in the ege capsule, so that in this gastropod the 
planktonic larva does not exist. : 
Mr. H. T. Burr gave ‘Results of Recent 
Studies of the Geology of the Boston Basin,’ 
and Mr. L. LaForge spoke on ‘The Relation 
of Dikes, Joints and Faults in Somerville, Mass.’ 
J. M. BourwELL, 
Recording Secretary. 
DISCUSSION AND CORRESPONDENCE. 
BODY BLIGHT OF PEAR TREES. 
In the spring of 1898 when preliminary studies 
with* apple canker were begun at this station 
a few inoculations were made in the limbs of a 
large pear tree with cultures of Sphxropsis, 
taken from cankered apple limbs. The fungus 
grew readily at all points of inoculation and 
produced dead sunken areas of the outer bark, 
similar to those that are so common on the 
trunks and larger limbs of pear trees. These 
definitely outlined and sunken areas of dead 
bark, commonly known as body blight, have 
long been thought to be due to the. action of 
the pear blight bacillus. However, it may be 
pointed out that body blight is preéminently a 
disease of the outer bark, while with pear 
blight the reverse is true since the cambium 
layer is first attacked. 
*Screncg, Vol. VIII., pp. 595 and 836. 
