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Transactions of the Canadian Institute, Vol. IX, 1912.

UNIVERSITY PRESS
TORONTO

A CONTRIBUTION TO THE MORPHOLOGY AND
BIOLOGY OF INSECT GALLS.

BY

A. COSENS, M.A.

Digitized by the Internet Archive
in 2010 with funding from
University of Toronto

http://www.archive.org/details/contributiontomo00cose

TO THE SENATE OF THE UNIVERSITY OF TORONTO:

Gentlemen :

I certify that the paper presented by Mr. A. Cosens, M.A., entitled ‘‘ A Contribution to
the Morphology and Biology of Insect Galls”, is satisfactory as a fulfilment of the thests re-
quirements exacted of candidates for the Degree of Doctor of Philosophy. Tt is a distinct
contribution to the knowledge of the subject.

(Signed) J. H. FAULL,

Associate Professor of Botany.
January 17th, 1913.

I hereby certify that the thesis above mentioned has been accepted by the Senate of the
University of Toronto for the Degree of Doctor of Philosophy, in accordance with the terms of
the Statute in that behalf.

(Signed) JAMES BREBNER,
Registrar.
March 29th, 1973.

TABLE OF CONTENTS.

PAGE

mn OL ACARI GANS. 6... 5. :0t alate ie.0\e Wei s.peraie a ons oyeios wings eee 299
i So LeDIIECr OWS) Gralla ey wislicicsy 0/4 vispuie sg ous, «6.8 bs4,0,0'* 0's ye Hes 303

ss Sep Ee RIGO pterOus; Gals o5 4 <)ii4is)cn)nedie’ae'dls)s'a.00 one oot eens 309

* PR MCSL ORS ANS. ood, sical dn nce Ciere Wein eimniae via wiae's o weiese x 316

“ ‘* Hymenopterous Galls—Fam. Tenthredinidz........... 327
NUMA AAO EL CANIS or is sleya sci andes ole Gales Ferre wena as BAS wees 337
Cnapesnine by sawiy Gall Producers)... ij. 3. icin ncn ae eeracceeees 338
Morphology of Hymenopterous Galls—Fam. Cynipide................. 339
em ORNS UE 55505 5c Wenags, « helareie ns CoM a a hie eS «A am alaliaC aly bene rd diel Save 356
EOSIN ia) arias eaten ofc Te bs Sims ns Hens a ar lee ocnhor a Nie! qt 8 Gone ses 357
Tee Repmmae of Gall Developments... .:0 sien isnde ced eteccnciues 358
Feeding Habits of the Larve of Gall Producers...............5.000005 361
Be aeeR MM IEMRCIE TARE SHEASIMILES 1 ced. 5s) icy he pay ool deem eel viale 24: <]h6 3,sile eels nals Ke tas 367
RAS HREM ah ore sie coed ac whic, ol Wife vat al edes cvcrasieial» euosers' shel dicy'ts lol's oss) ace lay apis ar sia ebevs 375

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TABLE OF CONTENTS.

PAGE

SINE FACES ORAM 0 6.5. 5) ctstal w/o wean: aceiel simeiscc.ais wesiaiwie 6x0 ss) eysle 6 299
vg Dat ed RMU CEES Cx oa. o 5! cask ofa: bal Wale, Whoa. sy>.«)aacejass. ew a6 'son v.68 303

ss Ree DIG OBLCKOMS: GANS 9.5 ciataa ss ccccicta of 0/ei6 0, ciara saintly ns « 309

ss SSDI PLCLOUS GANS 2 creicidis) cla Grarsreia, aio aieveo.8| aud elouaie’-)=tyisele iate aio 316

es ‘* Hymenopterous Galls—Fam. Tenthredinidz........... 327
IE ANTONE Oa ANN og 21027 tas «al oa a six ivan sos Bios, Umma aa. ge Be aoe are 337
Ovipasitine by Sawfly Gail Producers:. <j: 55 .t. ee cesses nee ew ecemsas 338
Morphology of Hymenopterous Galls—Fam. Cynipide................. 339
SURES RES RINU OLE? Z, OMG) 6555 icgsrs)s ols) x aes 00) ustlavelioye; eoaYe elias) of 810) anh o-9| shal acays, a. nt avai) aieh ey ss ere 356
MRE Ce LID aloo: acer llln: Ants whe Gwin Wiss 2% <ipis mya pele wi wtnicie.6 sights e's lap a2 357
The Beginning of Gall Development................+-. SO UCER CORA Ooo cle 358
Feeding Habits of the Larve of Gall Producers...............0.000005 361
eee aE RIPMMRIRCARNES SCUTINUNUG 74 10% 5, 28s, ds Fiass oe gieedi a. oa Simian wis tape 0:9 0/8 walmnele a pinye » 367
Mae MIM OTR 2205 (5 cchn'o'5 uke al's «Xia yale alone at are atoys L Peeeed ata hcg iain stats 375

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1912] MORPHOLOGY AND BIOLOGY oF INSECT GALLS 297

A CONTRIBUTION TO THE MORPHOLOGY AND BIOLOGY
OF INSECT GALLS.

By A. Cosens, M.A.

The earliest explanations offered to account for the origin of galls
are more or less fanciful, as must needs be, since nothing was known con-
cerning the reciprocal relations of host and parasite involved in their
life histories. Some of these theories dating from a less scientific age
are crystallized in the popular names attached to certain classes of these
structures. Thus the bristling masses of twigs, produced on several
species of trees by the stimulation of plant or animal parasites, are known
by some as ‘‘thunder bushes,” a term that implies the expenditure of
electrical energy in their origin. Also the more common name, ‘witches’
brooms,”’ indicates an equally imaginative explanation.

With the gradual advances of science much of the mystery surround-
ing galls has been dispelled, but they still present many interesting
problems. Among these are two standing out so prominently that they
seem to include all others. The first of these concerns the causes that
are operative in producing the gall. It is now generally recognized that
its origin is directly ascribable to the stimulation of a parasite, but the
problem still remains concerning the nature of the stimulus and the prin-
ciple governing the response. Concerning the nature of the stimulus,
Fockeu and his school ascribe it to mechanical means, while Kiister,
Kiistenmacher and others believe it to be referable to a chemical action.
With regard to the response by the host, the conventional view endows
the stimulated protoplasm with power to originate something foreign
and without a prototype in the normal host. But a view is developed
in this paper proposing an entirely different explanation, namely, that the
supposedly new types of organs, tissues, etc., are due to the awakening
of dormant characteristics in the protoplasm.

The second problem deals with the apparent philanthropy that char-
acterizes the host plant in its care for the parasite. Concerning this,
several explanations have been offered. The parasite may be simply
taking advantage of structures thrown out by the plant in its own de-
fence, or as Adler! figuratively expresses it, the besieger is making use
of the water in the moat in pushing forward the attack on the forti-
fications. Perchance, even what Darwin regarded as impossible has
taken place, and the plant is producing the gall entirely for the welfare of
the parasite. In opposition to this the theory is proposed by some

298 TRANSACTIONS OF THE CANADIAN INSTITUTE [VOL. Ix

investigators that in reality the host does derive benefit from the ab-
normal swelling since it has been the means of restricting the ravages of
the parasite to a limited area.

I have confined the subject-matter of this research to the Zoocecidia
including the Insecta and Arachnida. In the Insecta the following orders
are dealt with—Hemiptera, Lepidoptera, Diptera and Hymenoptera.
No attempt has been made to treat any one order exhaustively, but the
work was restricted to the living gall material at hand. Asa preliminary
to the botanical work, several seasons were spent in rearing the producers
in order that unquestioned identification could be assured of the various
forms studied.

Concerning the anatomy of our American galls, the only work done
previous to this is that by Cook,” who must be considered the pioneer
in this branch of the subject. The anatomical studies pursued are con-
sidered important as forming a foundation for deductions.

The recent investigations of Weidel*® on the early developmental
stages of Neuroterus have added valuable data to the ontogenetic work.
It is exceedingly necessary that some of the American species should be
worked out in the same manner, but before this can be done with assurance
of success, an American Adler must settle the questions concerning the
alternate generations of our native forms.

Special attention has been paid to the Sawfly and Lepidopterous
galls, since the anatomy of the former has hitherto not been dealt
with at all and the ontogeny only very inadequately. The latter have
also been neglected to nearly the same extent. The order Diptera and
the family Cynipide have presented the most interesting biological
phenomena, notably concerning the feeding habits and the nature of the
gall-producing stimulus, two factors that are closely parallel if not in-
deed identical in these two sections of the gall producers.

With the exception of Pachypsylla celtidis-mamma Riley all the
material was collected in the vicinity of Toronto. It was fixed in picro-
sublimate or Flemming’s weaker fluid and cut in series in paraffin or
celloidin. A double stain of safranin and hematoxylin was invariably
used.

The investigations described in this paper were carried on in the
Botanical Laboratories of the University of Toronto under the super-
vision of Prof. J. H. Faull, who suggested the subject and to whom I
wish to acknowledge my indebtedness for invaluable criticism and as-
sistance throughout. To Dr. C. D. Howe [ wish to express my obli-
gations for direction in the physiological experiments. My thanks are
also due to Mr. W. A. McCubbin, M.A., for valuable assistance in the
photography and to Mr. J. H. White, M.A., for normal material.

1912] MORPHOLOGY AND BIOLOGY OF INSECT GALLS 299

ORDER ACARINA.

The following species are described in this section :—

Order Acarina.
Fam. Eriophyide.

Eriophyes Sp. (Fagus grandifolia Ehrh.)

Eriophyes querci. (Quercus macrocarpa Michx.)

Eriophyes Sp. (Acer negundo L.)

Eriophyes Sp. (Populus grandidentata Michx.)

Eriophyes Sp. (Populus tremuloides Michx.)

Eriophyes Sp. (Prunus nigra Ait.)

Eriophyes abnormis. (Tilia americana L.)

Eriophyes serotine Beut. (Prunus serotina Ehrh.)

The numbers referred to are from ‘‘A Catalogue of the Phytoptid
Galls of North America,’’ by George H. Chadwick, 23rd Report of the
State Entomologist, New York State Museum, 1907.

Ertophyes Sp.
Chadwick’s No. 65
Host Fagus grandifolia Ehrh.

This gall occurs on the under side of the leaves of the host plant.
It is an erineum, white and frost-like at first, turning to a brown colour
at a later stage.

The anatomical structure of the interior of the leaf remains per-
fectly normal, the effect of the stimulation being confined to the epider-
mis. This produces a large number of unicellular, capitate hairs, re-
sembling miniature mushrooms, the resemblance to which is the more
striking since the stalks of the hairs are bulbous at the base, as shown
in Fig. 3. The hairs on the normal leaf are long, acicular and unicellular.
As this gall is produced with no increase in the number of cells in the leaf,
anatomically it stands as a simple type of ‘‘hypertrophy”’, the remaining
forms all exhibit the more advanced phenomenon of cell proliferation.

Eriophyes querct (Garman).
Chadwick’s No. 112
Host Quercus macrocarpa Michx.

In this gall, which is of the ‘‘dimple’”’ type, the depression is on the
under and the elevation on the upper side of the leaf. The hollow is
filled with a dense mass of brown pubescence. In rare cases the elevation
is on the under side of the leaf, when the pubescence then covers it.

The leaf blade in this case has become of nearly twice the normal
thickness. This has resulted from cell division which has occurred in
the tissues of both the palisade and the spongy parenchyma, producing
a compact mass of undifferentiated cells, entirely without intervening air
spaces. This tissue is shown in Fig. 6.

300 TRANSACTIONS OF THE CANADIAN INSTITUTE (VOL. Ix

The epidermis has responded to the stimulation by producing many
long, acicular, unicellular hairs, which are narrowed at the base. The
hairs are stellate on the normal leaf of the host, but are simple, uni-
cellular and acicular on its reproductive axis. The same feature is true
of Quercus robur var. pedunculata, and in all probability of the other oaks.
This appears to be a clear case, not of the production of a new type of
trichome, but of a reversion.

Eriophyes Sp.
Chadwick’s No. 2
Host Acer negundo L.

A shallow dimple on the under side of the leaf, filled with a white
pubescence.

In this gall as in the preceding species, the leaf blade has been very
much thickened by proliferation in the mesophyll. The cells produced
are circular in outline and of about the same size as those of the normal
spongy parenchyma. The hairs produced in this case not infrequently
consist of from 2 to 3 cells which are very much convoluted. They are
well shown in Fig. 4. The hairs on the normal leaf of the host are straight
or only very slightly curved, but the glandular, convoluted type of hair
is found on the inflorescence. Both the normal and abnormal hairs are
composed of the same number of cells.

Eriophyes Sp.
Chadwick’s No. 84
Host Populus grandidentata Michx.

A deep dimple gall with the convex part on the upper surface of
the leaf. The gall is light green above, with the contents of the depres-
sion dark red.

The cells produced by the palisade parenchyma can be distinguished
in this case from those arising from the spongy parenchyma. The
former are almost square in outline and placed in two very regular rows
immediately below the upper epidermis, and parallel with it. This
tissue can be seen in Fig. 2. The latter constitute a tissue made up of
cells which are circular to elliptical in outline. These cells are much
smaller than those produced by the palisade layer. The outgrowths
from the lower epidermis described in various ways as trichomes, granules,
etc., are in reality produced by a complicated folding, in which only the
lower epidermis and the spongy parenchyma participate, as shown in
Fig. 2.

A cross section of the gall shows a number of vascular strands, but
in my opinion the gall-producing stimulus only enlarges the veins that
are already present in the normal leaf; it does not originate a special
vascular system for the gall.

1912] MORPHOLOGY AND BIOLOGY OF INSECT GALLS 301

Eriophyes Sp.
Chadwick’s No. 88.

Chadwick considers this form, first described by Jarvis,* the same
as his No. 87. But the latter is characterized by a depression on the
under side of the leaf, the former by an elevation, so that the two are
constantly distinct.

Host Populus tremuloitdes Michx.

A dimple gall with the elevation on the under surface of the leaf.
The elevation is a lighter green than the surrounding normal leaf and
the folds that occupy the concavity are greenish-yellow or reddish in
colour.

In dealing with the anatomical structure it is to be noted that the
spongy parenchyma has in this case remained normal. The folds are
produced in the same manner as in the preceding species, except that in
this form it is the upper epidermis that undergoes the folding process.
The nature of this folding can be seen in Fig. 1.

Eriophyes Sp.
Chadwick’s No. 93.
Host Prunus nigra Ait.

A very much elongated pouch gall, greenish or whitish in colour,
found on the upper side of the leaf with the opening on the under side.

All the characteristics of the normal mesophyll have been com-
pletely altered in the affected part of the leaf. Its cells, which, with the
epidermis, constitute the wall of the gall, are larger than the normal and
are elongated parallel to the long axis of the outgrowth. The upper
epidermis which forms the epidermis of the gall has not been affected,
but the cells of the lower epidermis which line the gall cavity have become
much enlarged and in addition have produced a large number of closely
set trichomes which project into the gall cavity. The nature of these is
shown in the upper part of Fig. 5. These structures are often from 2 to
3, cells in length. Around the opening of the gall a circle of closely set
acicular hairs occurs. The hairs on the outside of the gall and on the
normal leaf are also of the acicular type. The vascular strands are much
larger than those of the normal leaf but appear to be simply the stimulated
normal veins.

Eriophyes abnormis (Garman).
Chadwick’s No. 144
Host Tilia americana L.

A very much lobed pouch-gall, usually on the upper side of the leaf,
found rarely on the under side. The opening which is on the opposite
side of the leaf to the pouch is surrounded by a dense growth of acicular
trichomes.

302 TRANSACTIONS OF THE CANADIAN INSTITUTE [VOL. 1x

The anatomical structure of this gall shows it to combine the char-
acteristics of a pouch-gall with a type in which the epidermis lining the
larval cavity is thrown into folds, as described in the case of the galls on
Populus. The foldings of the lining of the gall cavity often coalesce, and
practically divide the cavity into a number of compartments. Mor-
phologically this is one of the most highly differentiated of our Phy-
toptocecidia. The lining epidermis has produced a large number of
acicular, unicellular trichomes; these in some cases almost fill the cavities.
The hairs surrounding the gall aperture are of the same type, as are also
the normal hairs of the leaf. Glandular cells are much more abundant in
the gall tissues than in those of the normal leaf.

Eriophyes serotine Beut.
Chadwick’s No. 100
Host Prunus serotina Ehrh.

This is a club-shaped gall, produced on the upper side of the leaf
of the host. The aperture of exit, which is on the lower side, is sur-
rounded by fine white hairs. It varies in length from 5 to 8 mm. and at
a distance from the apex of about two-thirds the total length, it is nar-
rowed into a stalk with an average diameter of Imm. In color it varies
from green to a distinct red.

The stimulation has not produced very marked changes in the struc-
ture of the leaf near the origin of the gall. Apart from the fact that the
spongy parenchyma has divided more actively; the mesophyll is normal.
The upper epidermis of the leaf that forms the outer covering of the gall,
has its cell walls abnormally thickened. The lower epidermis that lines
the gall cavity has larger cells than the unstimulated epidermis, and from
these cells originate elongated, unicellular trichomes with bulbous bases.
The hairs on the normal leaf are acicular and unicellular. While the
cells in the neck of the gall are arranged in rows parallel to its length,
the larger cells that form the main body of the gall are not regularly
placed. The vascular strands pass up from the leaf at a distance of
about three cell layers from the gall cavity.

Summary.

In some forms the effect of the stimulation does not extend beyond
the epidermis, on which the producers are located, but in other species
it is transmitted throughout the mesophyll of the leaf.

The abnormal activity of the epidermis is expressed in the curving
and folding of the tissue as well as in the production by it of various forms
of trichomes.

In general, when the effect of the stimulation extends to the mesophyll
the distinction between the palisade and the spongy parenchyma is lost.
In place of these tissues a compact mass of uniform cells is produced.

1912] MORPHOLOGY AND BIOLOGY OF INSECT GALLS 303

The types of the galls constitute a clear phylogenetic series from the
simple erineum to the well developed pouch-gall. The distinction be-
tween the different members of this series is largely a difference in degree
rather than in kind, and seems to be explainable on the assumption of a
gradually increasing intensity of stimulus from the lowest to the highest
member of the series.

The literature of this group of galls contains a number of state-
ments, to the effect that the host plant under the influence of the gall
stimulus can originate entirely new types of hairs. While it is true, as a
general rule, that hairs produced by an organ under such a stimulus differ
from those originated by that organ under normal conditions, yet in such
cases I have found that the abnormal type of hair is being produced on
another part of the host plant. Thus the curiously convoluted, glandular
hairs, originating in the dimple galls on the leaves of Acer negundo L.,
are duplicated exactly in the hairs occurring on the reproductive axis
of the same plant, and the long acicular hairs composing the brown pubes-
cence that fills the concavities on the leaves of Quercus macrocarpa
Michx have their exact counterparts in those produced on the flowering
axis of that plant. In the former example the normal hairs on the leaves
of the host are straight and acicular, in the latter they are of the stellate
type. -

ORDER HEMIPTERA.
The following Hemipterous galls have been studied :—
Fam. Aphidide.

Gall on Populus balsamifera L. (Unclass.).

Hormaphis hamamelidts Fitch.

Hamamelistes spinosus Shimer.

Aphid Corrugations on Birch.

Pemphigus vagabundus Walsh.

Pemphigus rhots Fitch.

Chermes abietis Chol.

Chermes floccus Patch.

Fam. Psyllide.

Pachypsylla celtidis-mamma Riley.

Aphid Gall (Unclassified),
Host Populus balsamifera L.

A pouch-like gall on the under surface of the leaf, produced by a
fold in the blade near the base of the midrib. One edge of the fold is
attached along this midrib. The slit-like opening, which is on the upper
surface of the leaf, extends the full length of the gall. This species re-
sembles very closely the gall produced by Cecidomyia majalis Bass. The
general structure is shown in Fig. 7.

304 | TRANSACTIONS OF THE CANADIAN INSTITUTE [VOL. Ix

“= Dimensions:—Length along line of attachment to midrib, 10-12 mm. ;
Width, 4-5 mm.

In the part of the leaf blade that forms the gall all resemblance to
the normal mesophyll has disappeared. A compact mass of tissue has
taken its place, the cells of which are much larger than normal meso-
phyll cells. Towards the interior of the gall the cells become smaller
and richer in protoplasmic contents. The upper epidermis forming the
interior of the gall remains practically normal, except that it produces
longer and more abundant trichomes than when unstimulated. These
trichomes are usually three cells in length. A cross section of this gall
shows two small groups of cells with porous laminated sclerenchymatous
walls, one of which is situated near the midrib and the other exactly op-
posite on the other side of the gall opening. Thus each side of the gall
aperture is bordered by a band of sclerified cells, as shown in the trans-
verse section of Fig. 8.

Hormaphis hamamelidis Fitch.

Host Hamamelis virginiana L.

The gall formed by this species is found on the upper side of the leaf
of the host, but the larve escape from an opening on the under side.
The mature gall is conoidal in shape with the apex usually slightly bent
over. General structure is illustrated in Fig. 12. A circular ring of
tissue covered with pubescence surrounds the gall opening which is shown
in Fig. 12.

Dimensions:—Average length of gall 10.5 mm.; diameter at base
4 mm.

The gall is composed of small cells placed close together, forming a
compact and very uniform tissue. The cells are arranged with their
longer diameters pointing in the direction of the gall apex. In a longi-
tudinal section the vascular strands are seen to pass up each side at a
depth of about three cells from the gall cavity. The beaks of the larve,
often found imbedded in the wall of the gall, were inserted far enough to
almost reach these vascular strands. The hairs that surround the gall
aperture are acicular and unicellular.

Hamamelistes spinosus Shimer.
Host Hamamelis virginiana L.

The galls in this species are modified flower buds. These are some-
what elliptical in outline with gradually tapering stalks. They are
covered with spines, which are usually curved. The opening is situated
at the union of the stalk and the gall proper. This opening is funnel-
shaped and is surrounded by a circular ring of tissue as in the preceding
species on the same host. The pubescence is absent in this case.

1912 MORPHOLOGY AND BIOLOGY OF INSECT GALLS 305
9

Dimensions :—Average length including stalk 21 mm.; average
width 10 mm.

This gall is covered by an unusually small-celled epidermis. The
spines that are so noticeable a feature are found to consist of projections
of the epidermis, filled with cells in continuity with the mesophyll. The
cells of the gall are almost perfectly circular in outline and packed to-
gether very closely. This tissue is very uniform except in the four or
five ayers adjoining the gall cavity. In that zone the cells are smaller
and richer in protoplasmic contents, constituting a fairly well marked
nutritive layer.

In cross section of the gall about thirty main fibro-vascular bundles
are cut; these are comparatively large and situated near the larval cavity.
Two of these have been cut in the section shown in Fig. 10. Other
smaller strands are cut further out. The gall receives all the fibro-
vascular strands that, under normal conditions, would have passed up
into the flower. The interior of both this and the preceding species is
almost perfectly glabrous.

Aphid Corrugations on Birch.

Betula lenta L.

Hosts sen alba var. papyrifera (Marsh) Spach.

The primary folds in the leaf that form this gall run parallel to the
main veins, with the latter as boundaries between them. Their crests
are on the upper side of the leaf, while the hollows which form the larval
chambers are on the under side. The primary folds are divided into
secondary folds, and these again into depressions resembling minute
Acarina dimple-galls. This complex arrangement is conditioned entirely
by the veining of the leaf, since each fold, primary or secondary, is sup-
ported along its edges by veins. The folding can be seen in Fig. 9.

The anatomical characteristics of these galls show that the folding
of the leaf has not entirely changed the structure of its normal mesophyll.
Around the gall cavities the spongy parenchyma is nearly normal through-
out and the palisade layer is recognizable in different places. The cells,
however, are considerably larger than the cells of the normal mesophyll.
The cells of the lower epidermis, that form the lining of the gall cavities,
are well filled with food materials for the larvae. The supporting veins
on each side of the fold send out branches that supply the gall with an
adequate vascular system.

Hormaphis hamamelidis Fitch and Hamamelistes spinosus Shimer,
as worked out by Pergande,” show that they inhabit alternately Betula
mgra L. and Hamamelas virginiana L.

306 TRANSACTIONS OF THE CANADIAN INSTITUTE [voL. Ix

The galls on the birch leaves are produced by the fourth genera-
tion of Hamamelistes spinosus Shimer. Pergande described them as
““pseudo-galls or corrugations”’.

The witch-hazel galls produced by the stem-mother of this species
are plentiful in this locality, but Betula nigra L. is not found here. The
Aphids have consequently been compelled to extend their list of food
plants to include B. lenta L. and B. alba var. papyrifera Spach.

Pemphigus vagabundus Walsh.
Host Populus deltoides, Marsh.

All the leaf rudiments of the terminal bud appear to be concerned
in the production of this gall. Yet it is in reality a large pouch-gall with
its wall thrown into smaller secondary folds. The apex of the stem, from
which the gall originates, is usually swollen to nearly twice its normal
diameter. These galls often remain on the host plant until the next
season’s galls begin to appear.

The cells composing this gall form a compact and fairly uniform
tissue and a nutritive layer is not clearly differentiated. About one-
third of the thickness of the gall wall, on the side next the larval chamber,
however, is composed of cells that are somewhat larger than the remain-
ing cells. The epidermal cells, lining the gall cavity, are elongated into
short trichome-like structures. The phyllome origin of this gall is re-
vealed by the presence of well defined stomata on its epidermis. These
structures are numerous and appear to be quite normal. Glandular
cells are plentifully distributed. Vascular strands pass irregularly
throughout the wall of the gall.

Pemphigus rhots, Fitch.
Host Rhus typhina L.

A balloon-shaped gall with the regularity of its outline destroyed
by the elongated lobes that cover its surface. A gall is shown in Fig. 14.
The epidermis is slightly pubescent and coloured red, shading into yellow
and green. It originates from the under side of the leaf, and the point
of attachment on the upper side is indicated by a small papilla covered
with a dense pubescence. These galls vary in size from very short types
less than I cm. to those that are 4 to 5 cm. in length.

In the part of the leaf blade folded to form the gall, the mesophyll
has been entirely changed. The effect of the stimulation has even de-
stroyed the normal characters in the mesophyll for some distance from
the point of attachment of the gall. The gall consists of a compact
tissue composed of cells considerably larger than the normal cells of the
mesophyll. The cells of this tissue are arranged in layers parallel to the
epidermis of the gall. The vascular strands are situated about four cell
layers in from the gall cavity. In all pouch-galls the tracheary tissue is

1912] MORPHOLOGY AND BIOLOGY oF INSECT GALLS 307

composed of the ordinary vascular elements of the normal leaf that have
been stimulated to increased activity. There is not a special tracheary
system originated for the gall. In the galls the strands occupy a definite
position, since in the normal leaf they occupy a definite place in relation
to the spongy and the palisade parenchyma. Large glands are present
in the gall tissue, as shown in Fig. 14. A gland is found invariably asso-
ciated with a fibro-vascular strand and seems to have its counterpart in
the very small gland that runs through each vein of the normal leaf.
In some cases the abnormal glands have acicular trichomes projecting
into their cavities.

Chermes abietis Chol.

Picea abies (L) Karst.
Picea mariana (Mill) B.S.P.

A polythalamous gall produced by the swelling of the base of the
young shoots. Since the twigs are not usually killed the galls are sur-
mounted by a variable length of normal stem. The galls in general
vary from conoidal to nearly spherical in shape, but in some cases, owing
to the stimulation not having affected the entire circumference of the
stem, the gall does not extend completely around it and is consequently
less regular in outline. The surface of the gall is covered with the en-
larged bases of the aborted needles. These give a faceted appearance to
the gall and produce a likeness to a miniature pineapple.

Dimensions:—Longer diameter 2-3 cm.; shorter diameter I-2 cm.

The gall in this case is a joint production of the cortex of the stem
and the bases of the leaves of the host. The cells of the epidermis, lin-
ing the gall cavities, in some cases have been prolonged to form very short
trichome-like structures. The hairs at the aperture of exit, as seen in
Fig. 11, are composed of one or two cells.

The resin ducts that occur in the normal cortex are found consider-
ably enlarged in the gall. In addition to these, there are out near the
gall periphery numerous smaller resin ducts, as shown near the margin
of Fig. 11, that do not have corresponding structures in the unstimulated
tissues. These additional ducts pass in from the swollen bases of the
aborted leaves. A cross section near the base of these leaves cuts from
four to six resin ducts, while a normal leaf does not contain more than
two of these structures.

Hosts{

Chermes floccus, Patch.
Host Picea mariana (Mill) B.S.P.
In this species the gall is produced by the swelling of the entire shoot.
In comparison with the former species, the leaves are little, if any,
swollen at the base but are more numerous on the gall than on an equal

308 TRANSACTIONS OF THE CANADIAN INSTITUTE [VOL. Ix

length of normal stem, owing to the shortening of the stem axis. The
larval cells are in the cortex of the stem at the bases of the needles.

Dimensions :—Average length 2-6 cm.

The abnormal development of the cortex, especially that part con-
tained in the wings on the stem, produces the entire mass of this gall.
The stimulation has increased the number of resin ducts in the cortex.
Several cross sections of galls were compared with corresponding sections
from normal stems. The average number of resin ducts in the abnormal
to that in the normal was in the proportion of 20 to 12. The smaller
accessory resin ducts are shown in Fig. 13. In every section examined
the additional ducts were in an irregular circle outside the normal ducts.
The ducts produced under stimulation were larger than the corresponding
normal ducts, but those that were found only in the abnormal tissues were
smaller than the normal structures.

Fam. Psyllide.
Pachypsylla celtidis-mamma Riley.
Host Celtis occidentalis L.

A complicated form of pouch-gall produced in the mesophyll of
the leaf of the host. On the upper surface of the leaf the gall is indicated
by a decided depression in the centre of which is a slight elevation that
marks the opening of the gall. The part projecting from the lower
surface, is oblate-spheroidal in shape, attached to the leaf by a slightly
tapering cylindrical stalk. The average number of galls found on a leaf
is usually about ten, but in some cases much higher. The surface of the
gall is smooth except for a few fine scattered hairs, glaucous and greenish-
yellow in colour. .

Dimensions:—Height from point of attachment 6-7 mm.; width
7-8 mm.

The anatomical structure of this gall shows it to be a more complex
type than any other of the Hemiptera discussed in this paper.

Besides the folding of the leaf the blade has been further changed
in thickness and in the character of the cells. The production of the
greater part of the abnormal tissue is due to a wide, well differentiated
cambium layer, that extends right across the gall and at its margin
passes into the tissues of the normal leaf between the palisade and the
spongy parenchyma (Fig. 15). The larval chamber is lined by this
cambium sheath which thus functions as a nutritive layer. Bordering
this zone is a well developed protective tissue composed of cells with
uniformly thickened walls. The sclerenchyma is laminated and pene-
trated by branched canals, presenting the same character as that found
in the galls of the Cynipide.

1912] MoRPHOLOGY AND BIoLoGy oF INSECT GALLS 309

Outside of this protective zone lies the chief mass of the gall, com-
posed of thin-walled irregularly shaped cells, as illustrated in Fig. 15.
Typical cells of the protective sheath are also found scattered throughout
this tissue. As the gall becomes older these cells increase in number.

Summary.

These galls are characterized by a folding and wrinkling of the leaf
when they occur on that organ; in this particular they resemble the
Phytoptocecidia. This common characteristic is due to the fact that in
the orders Acarina and Hemiptera the stimulation is all from one side.
The spherical type of the Cynipide is produced by a stimulus equally
disseminated in all directions.

The tendency to produce trichome structures from the stimulated
surface, so marked a characteristic of the Acarina forms, is in this group
practically absent; the only hairs produced are those surrounding the
gall apertures.

In most species of both groups there is little differentiation of tissues,
so that the protective sclerenchyma zones mentioned in the genus
Pachypsylla and the unclassified species on Populus balsamifera L.
mark a distinct advance on the specialization attained by the Acarina
galls and an approximation to the more complex types found in the
orders Diptera and Hymenoptera.

The increased number of resin ducts in the tissues of the Conifere
stimulated by species of the genus Chermes is an important feature of
these galls.

ORDER LEPIDOPTERA.

The Lepidopterous producers referred to in this paper occupy the
following positions in Dyar’s List of North American Lepidoptera,
United States National Museum, Washington, 1902.

Fam. Sesiidz.
Memythrus tricinctus Harris.
Fam. Tortricide.
Eucosma scudderiana Clemens.
Fam. Gelechiide.
Gnorimoschema gallesolidaginis Riley.
Gnorimoschema galleasterella Kellicott.
Fam. Tineide.
Stagmatophora ceanothiella Cosens.
The host plants of the various species are :—

Memythrus tricinctus Harris.

Populus tremuloides Michx.

310 TRANSACTIONS OF THE CANADIAN INSTITUTE [VOL. 1

Eucosma scudderiana Clemens.
Solidago canadensis L.
Solidago serotina var. gigantea Gray (seldom).

Gnorimoschema gallesolidaginis Riley.

Solidago canadensis L.
Solidago serotina var. gigantea Gray.
Solidago rugosa Mill (seldom).

Gnorimoschema galleasterella Kellicott.

Solidago latifolia L.
Solidago cesia var. axillaris Gray (seldom).

In speaking of the host plant of this producer Busck” makes th
following statement: ‘‘I have before me specimens from Miss Clark
which were unquestionably bred from the white wood-aster, Aster divar
catus L. (A. corymbosum Ait.) near Boston.’’

Stagmatophora ceanothiella Cosens.

Ceanothus americanus L.

Tucker® states that C. ovatus Desf. is also a host plant of this specie

The following dates taken from records of specimens represent ay
proximately the time of emergence of the moths:

Memythrus tricinctus Harris—July 4 to 8.

Eucosma scudderiana Clemens—June 8 to 20.

Gnorimoschema gallesolidaginis Riley—August 5 to 15.

Gnorimoschema galleasterella Kellicott—August 12 to 19.

Stagmatophora ceanothiella Cosens—June 23 to 30.

The two species of the genus Gnorimoschema pass the winter i
the imago stage but Eucosma and Stagmatophora in the larval forn

Several galls of the Eucosma moth were opened December 1
and the data collected were as follows:—The larva was in a dormar
state in the portion of the stem of the plant immediately below the gal
Before passing into this inactive condition the larva had carefully pr
pared for the emergence of the imago from the gall. The wall of tt
gall cavity had been eaten through until the part remaining was thi
enough to permit the passage of light. The exit thus prepared we
located at the upper end of the gall and was on an average 2 mm. i
diameter.

A silk lining covered the whole of the interior of the gall and
partition of especially strong silk crossed the cavity just opposite tk
opening mentioned above. This partition did not pass straight acro:
the gall but was found always in a slanting direction. It was attache
to the gall wall just above the aperture and was always higher on thz
side.

1912 MoRPHOLOGY AND BIOLOGY OF INSECT GALLS 311
9

Galls produced by the Stagmatophora moth were examined a few
days later and the larve were found to be passing the winter under
very similar conditions to those described in the case of the Eucosma
species. The Stagmatophora larve were not perfectly dormant, how-
ever, and soon became quite lively in a warm room. They were found
invariably in the gall cavity with their heads a short distance below the
prepared exit. This had been constructed as in the preceding case and
was situated at the same place. The silk lining covered the interior of
the gall but in this case was gradually narrowed to the size of the hole
around the edges of which it was attached. As the plant stem was not
hollow above the gall, the roof of the gall cavity occupied much the same
position as the slanting silk partition in the Eucosma gall.

The silk lining common to both of these galls helps to prevent the
loss of moisture and the consequent desiccation of the larva.

The cross partition of the Eucosma gall and the tapering neck found
in the lining of the Stagmatophora species seem to have the function in
common of guiding the occupant of the gall to the prepared exit.

Memythrus tricinctus Harris.

This form has hitherto never been considered a true gall maker—
just why it is difficult to understand. Beutenmiiller*? reports it as
a borer in stems of poplar and willow and in galls of Saperda concolor.
I have repeatedly, however, bred this species from swellings on the
smaller branches of young trees of Populus tremuloides Michx. These
swellings were spindle-shaped, gradually tapering at each end to the
size of the normal stem. In external form they were quite typical galls
of the Lepidopterous class.

A comparison of the larval chamber of this gall with that of the
Eucosma species shows that the two have certain features in common.
Thus, although the opening in the stem made by the young larva in
entering closes in the Eucosma gall, but not in this one, it can be found
in the earlier stages of both. The silk lining in the larval chamber is not
present, but the slanting silk partition has a similar structure and position
to that found in the Eucosma species. This partition shuts off the per-
manent larval entrance from the part of the chamber in which pupation
takes place. The place of exit has the same relation to this partition as
that described in the Eucosma gall. The opening is prepared in the same
manner. The larva eats through the wall of the gall until the part re-
maining is translucent just as in the case of the Eucosma or Stagmato-
phora forms. The larve in the two latter species prepare this opening
in the fall, but the Memythrus larva does not complete it until shortly
before pupation in the spring.

312 TRANSACTIONS OF THE CANADIAN INSTITUTE [VOL. Ix

Dimensions :—As the size of the gall varies with that of the stem,
an average of several specimens was taken. Length, 60 mm.; width, 20
mm.; diameter of normal stem at place of location of the gall, 12 mm.

A cross section of this gall, when compared with the normal stem,
shows an abnormal thickening of the cortex and an increase in width of
the bast and wood. Throughout the annual rings of wood are bast
fibres, sometimes arranged irregularly in patches, in other cases forming
fairly definite zones on the outside of the annual ring. The fibres are
shown in Fig. 16.

Eucosma scudderiana Clemens.

“The galls are at the top of the main stems of the plants, usually
within the flowering panicle, rarely on the branches of the panicle;
usually but one gall on a plant, occasionally two, rarely three.

“The galls are spindle-form, varying in size from 10X16 mm. to
1228 mm.; diameter of stem below gall from 4 mm. to 5 mm.; the
average of ten galls collected in ten seasons, 100 specimens, was 93 X21}
mm., diameter of stem below gall 5 mm.’’—Brodie.”

The gall mass in this case is produced from the vascular bundles
and the intervening parenchymatous strands. When the larva enters
the stem it first eats out the pith. After the exhaustion of this source of
nourishment, its food is supplied by the radial thickening of the bundles
into the gall cavity. The secondary wood elements thus formed remain
somewhat parenchymatous and can scarcely be distinguished from the
cells of the medullary rays. The cortex is somewhat thicker than that
found in the normal stem but this is not a very marked feature in the gall
production.

In the normal stem of Solidago canadensis L. there is a gland opposite
each bundle both on the side of the cortex and on that of the pith. The
glands in the cortex of the gall are the same in number but are very much
larger (Fig. 21). Likewise they are not regularly arranged but grouped
two or three together. This is due to the fact that since some of the
bundles have developed much more rapidly than others, their alignment
has been destroyed.

The glands corresponding to the normal inner row were not found
in the gall. This is accounted for by the early removal of the pith of
the stem by the producer larva.

Gnorimoschema galiesolidaginis Riley.

““Galls usually on the lower third of the stems of Solidago cana-
densis L. occasionally on the upper third, rarely at the summit of the
stem. The galls vary in form from spindle-form to prolate and oblate
spheroid; and in size from 10X21 mm. to 18 X30 mm.

1912] MorRPHOLOGY AND BIOLOGY OF INSECT GALLS 313

“Some observers say the interior of the gall is lined with silk. I
have never found this, but preparatory to the exit, the mature larva be-
fore pupating constructs a silken hammock in the upper end of the gall,
and opposite the aperture of exit. The larva resting in this hammock
bites out a hole to the epidermis of the gall which is carefully left. The
hole is bevelled towards the outside, and then neatly filled up with the
material gnawed out, mixed with a silk-like substance, doubtless from a
gland, which forms a tight-fitting, hard plug which cannot be pushed in
from the outside but is easily pushed out from the inside.’’—Brodie.”

The anatomical features of this gall are very similar to those de-
scribed in the Eucosma species. The gall mass is produced by the radial
increase in thickness of the bundles and the growth into the gall cavity
of the intervening parenchymatous strands seen in Fig. 20. There is
greater proliferation of the cortical tissue in this case than in that of the
Eucosma gall and the cells produced are much larger than those found
in the normal stem.

The remarks concerning the gland production and distribution of
the preceding species are also applicable to this form.

Gnorimoschema galleasierelia Kellicott.

“In a collection of galls made May 29, 1890, a few miles north of
Toronto, most of them were at the top of the stem, surmounted by a few
leaves, occasionally but one, usually two. The galls at this date seemed
to be mature, subtriangular, corresponding to stem of plant; from 20
mm. to 32 mm. long, and from 10 mm. to 15 mm. diameter. In size,
form and structure the galls closely resemble the galls of G. gallesolida-
ginis Riley. Rarely they occur on the middle and lower third of the
stem of the plant.’’—Brodie.”

“The gall produced on Solidago cesia var. axillaris Gray by this
producer is quite unlike the S. latifolia gall in appearance, but as both
galls are merely spindle-shaped enlargements of the stems of the host
plants, this difference in outward form can easily be explained. The
_ glaucous, terete and slender stem of S. cesia produces a gall with glaucous
epidermis, circular in cross section and gradually tapering towards each
end. On the other hand, the smooth, angled and comparatively thick
stem of S. latifolia gives rise to a gall with smooth epidermis, somewhat
triangular in cross section. This gall has also a greater diameter and
tapers more abruptly than the S. c@sia gall.’’-—Cosens.”

The anatomy of this gall presents the typical structure of a gall of
the Lepidopterous class. The cortex of the stem does not play an im-
portant réle in the production of the abnormal tissue; but when the
host plant is Solidago latifolia L. the gall cortex is thicker than that of
the normal stem. As in the case of the gall produced by G. gallesoli-

414 TRANSACTIONS OF THE CANADIAN INSTITUTE [VOL. Ix

daginis Riley, the bundles and the medullary rays are extended into the
gall cavity and furnish the principal part of the tissue proliferation.
Only a very shallow seam of normal wood is found in the galls produced
on S. ces a var. axillaris Gray.

Glands do not occur in the normal stems of either of the host plants
and were not found in the tissues of this gall.

A section through the aperture of exit of a gall on S. cesta var.
axillaris Gray showed that the edges of the opening had been prepared
by the larva for the reception of the “plug” that closed the opening.
The sides of this aperture, roughened by the gnawing away of the tissue,
would not admit of the “plug” fitting tightly and at the same time
slipping out easily when occasion required. Consequently the gnawed
surface is smoothed over by a layer of material that presents a perfectly
even surface. This levelling-up material is uniform in character and
does not show any trace of vegetable débris. At right angles to its
free surface, an effect resembling checking takes place, a change that it
has probably undergone in drying. This is illustrated in Fig. 22.

The ‘‘plugs”’ of the galls produced by the genus Gnorimoschema
have been reported as consisting of silk and material gnawn out by the
larve in preparing the openings. My observations incline me to the
belief that the material, forming the plug and lining the opening, con-
sists entirely of an exudation from the larva. It seems to be a plastic
silk-like substance.

Stagmatophora ceanothiella Cosens.

‘These abnormal growths are found commonly on a main stem, but
rarely on a branch. The flower cluster is sometimes entirely aborted,
but usually only partly so, the lower pedicels in the cluster remaining
normal. In the majority of cases this gall is terminal, but in a few in-
stances the stem was found to project a short distance beyond it.

“The gall has the relatively simple structure of a spindle-shaped
enlargement of the stem. In length it varies from 10 to 15 mm. and
in greatest width from 5 to 8 mm. It is roughened on the outside by
the stumps of the aborted branches. On account of the shortening of
the stem axis and the consequent crowding of the nodes, these branches
are more numerous on a gall than on a corresponding length of normal
stem. This gives the gall a gnarled surface and forms a strongly pro-
tected case for the larva. The gall in some cases is surmounted by a
tuft of leaves growing from its apex.

“The aperture through which the moth escapes from the gall is made
always near the upper end.’’—Cosens.*

1912] MORPHOLOGY AND BIOLOGY OF INSECT GALLS 315

As in the preceding galls described, the principal part of the gall
tissues in this species is originated from the vascular bundles and paren-
chyma strands (Fig. 17). The latter are very wide and the abnormal
cell division is more marked in them than in the bundles. The wood
elements produced remain undifferentiated and pith-like. The cuticle
of the gall epidermis is much stronger than that found in the normal stem.
The epidermis itself has responded to the stimulation by the production
of an extra layer of cells. The cortex of the gall contains approximately
one-third more cell layers than the normal cortex as seen in Fig. 18.

The normal stem of Ceanothus americanus L. contains glands in
the cortex. These are fairly regularly spaced around the stem but are
larger and more numerous at the nodes. Glands occur also in the pith
of the stem, the petioles of the leaves and the reproductive axes. But in
parts of stems, contiguous with galls, though glands occur in the pith there
are none in the cortex, except at the nodes. Glandular cells, however,
are plentiful in the cortex of such stems.

A cross section of a gall shows larger and more numerous glands
than a corresponding section of the normal stem. The probable ex-
planation of this is that owing to the shortening of the stem axis, nodes
are cut more frequently. In the gall cortex there are also narrow, elong-
ated, glandular cavities, that do not seemingly correspond to anything
seen in the normal stem. They require further elucidation. They are
in groups each containing three or four glands, as illustrated in Fig. 19.

Summary.

The galls are all of a comparatively simple type, for while there
is considerable proliferation in the tissues there is little differentiation.
The medullary rays and vascular bundles respond the most readily to
the gall stimulus, yet cell division takes place in the epidermis of the
species Siagmatophora ceanothiella Cosens.

The highly specialized habits of the larva, developed in caring for
the welfare of the imago, make the group very interesting. Thus in
_ each of the forms studied provision is made by the larva for the emergence
of the moth from the gall. These habits are seen at different stages of
development. In Stagmatophora ceanothiella Cosens and Eucosma
scudderiana Clemens the gall wall is simply gnawn partly through, while
in the Gnorimoschema genus an aperture of exit is carefully prepared
and plugged. These different methods of procedure are remarkably
suited to the habits of the insects. In the former a plugged exit would
not be suitable as the insect winters in the larval condition and the drying
of the gall would prevent the plug from slipping out easily. In the latter
the galls are still green when the insect becomes mature and the plug
mechanism is preferable. It is clear then that in these galls the producer

316 TRANSACTIONS OF THE CANADIAN INSTITUTE [VOL. Ix

is much more active in providing for its own welfare than in the higher
types and the plant renders a relatively smaller amount of assistance.
As the stimulation of the animal participant becomes more effective, the
plant is coerced into providing more suitable conditions for the maturing
of the producer, which consequently becomes less active on its own be-
half and more dependent on the host.

While glands are invariably larger in the gall tissues than in the
corresponding normal stems, Stagmatophora ceanothiella Cosens fur-
nishes the only example where there is a distinct increase in the number
of glands.

An unusual cell division occurs in the species S. ceanothiella Cosens
and G. galleasterella Kellicott. The daughter cells are in clusters,
usually four in number, clearly showing they have originated from a com-
mon progenitor. The septations between the cells are always very
straight and the elongated nuclei are pressed closely against the division
walls. This form of mitosis produces only a very small portion of the
gall tissues in these species, but in the Dipterous gall Neolasioptera per-
foliata Felt (Fig. 23) it originates nearly the whole mass. This form will
be referred to again and the cell division illustrated in the part of this
paper dealing with Dipterous galls.

As I have repeatedly found the opening through which the larva
of Eucosma scudderiana Clemens has entered the stem, it is certain that
this Lepidopterous producer always oviposits on the outside of the host,
and this may prove to be true of the entire group.

ORDER DIPTERA.

The anatomy of the following species is considered :—
Order Diptera,
Fam. Cecidomyide.
Cecidomyia bulla Walsh.
Cecidomyia balsamicola Lintner.
Cecidomyia impatientis O.S.
Cecidomyia majalis O.S.
Cecidomyia ocellaris OS.
Cecidomyia pellex O.S.
Cecitdomyia triticoides Walsh.
Lasioptera corni Felt.
Lasioptera impatientifolia Felt.
Neolasioptera perfoliata Felt.
Rhabdophaga batatas Walsh.
Rhabdophaga strobiloides Walsh.

1912 MORPHOLOGY AND BIOLOGY OF INSECT GALLS 17
9 3

Fam. Trypetide.

Eurosta solidaginis Fitch.

The classification is as far as possible in accordance with Aldrich’s
catalogue of North American Diptera, Smithsonian Institute, Washing-
ton, D.C., 1905.

Cecidomyia bulla Walsh.
tec 2 elianthus decapetalus L.
Helianthus divaricatus L.

‘“‘Galls found usually on the stem, often from leaf axils, occasionally
on petiole and midvein of leaf, rarely on flower disc, protruding from
between scales of involucre.

“The galls are attached by an ample base and are very irregular in
form and position, usually somewhat compressed, varying from nearly
spherical to flask and cone shaped and from equilateral triangular to
spur-shaped.

“Dimensions:—The average of twenty galls was, base, 5.5 mm.
thick and extending 8 mm. from stem.’’—Brodie.'®

On the side of the stem from which the gall originates the vascular
bundles are very irregularly arranged and elongated transversely in the
direction of the gall axis. From these bundles vascular strands pass
out into the gall mass. The principal part of the tissues in this gall
originates from the medullary rays, as can be seen in Fig. 39. When
the cortex of the stem passes into the abnormal cortex it becomes con-
siderably thicker; this is due chiefly to the increase in size of the cells as the
number of rows remains approximately the same as in the normal cortex.

Glands are found in the normal cortex of Helianthus; they are
arranged in such a manner that a gland is placed opposite each fibro-
vascular bundle. These glands are very much larger in the abnormal
cortex of the gall. Besides these glands there are others that have
not a counterpart in the normal stem. These are elongated in the
direction of the gall axis and are most abundantly produced in the
vicinity of the fibro-vascular strands.

There are practically only two zones represented in this gall, the
epidermal and the parenchyma. The cells of the latter become slightly
smaller towards the larval chamber but a well defined nutritive layer is
not differentiated.

Cecidomyia balsamicola Lintner.
Host Abies balsamea (L) Mill.

A monothalamous gall formed by a folding of the leaf with the upper
surface on the inside (Fig. 29). An enlargement ellipsoidal in shape is
thus produced. The needles affected are near the apex of the stem and
the galls are situated close to the base of the needles.

318 TRANSACTIONS OF THE CANADIAN INSTITUTE [VOL. IX

Dimensions:—Diameter along the leaf average 2.5 mm.;_ shorter
diameter, average I.5 mm.

The abnormal part of the leaf differs very markedly from the normal.
The cuticle is entirely absent from the upper surface of the leaf that
lines the interior of the gall. While the epidermis is uniformly thickened
the normal cells have much heavier outer walls. The normal meso-
phyll cells are circular to widely elliptical in outline (Fig. 28), but the
abnormal cells are very much elongated (Figs. 29, 30). Since the en-
dodermis is poorly developed the mesophyll is not clearly separated from
the pericycle. In this region the transfusion tissue is well represented,
but the non-pitted parenchyma is not so abundant as in the normal
(Fig. 31). The abnormal resin ducts are increased in size and have the
protective layer irregularly developed.

In tabulated form is given a comparison of the anatomical structure
of a normal leaf with one infected by the gall producer Cecidomyia bal-
samicola Lintner and one from a witches’ broom produced by Aicidium

elatinum on Abies balsamea (L.) Mill.
The data for the last named were obtained from Anderson.?

Leaf Structure.

——

Cuticle

Normal Leaves.

Well developed on

Affected with
Zicidium elatinum

Present but less

Affected with Ceci-
domyia balsamicola
Lintner.

Abnormally thick-

both surfaces. developed. ened on the lower
surface (outside of
the gall), not de-
veloped on the

upper (inside).
Epidermis The outer are Epidermal cells On the ‘outside of
thicker than the in- more irregular than the gall the epider-
side walls. Both in normal; less mal cells are ir-
are laminated and _ thickened and sel- regular and have
perforated bypores. domlaminatedand uniformly thicken-
provided with pore ed walls; they are
canals. not clearly lami-
nated but pore
canals are more
plentiful than in
the normal. The
inner epidermis is

not thickened.
Stomata More numerous on Like the normal The same as the
the lower than on but fewer on each preceding affected

the upper leaf sur- surface. by the fungus.

face.

Hypoderm Well developed at Hypodermal cells Cells irregularly de-
the basal half of the fewer, but usually veloped, invariably
leaf. larger, thicker curved and com-

walled and more
irregular than in
norma! leaves.

pletely filled with
laminated scleren-
chyma.

1912]

Mesophyll

Resin Canals

Endodermis

Transfusion Tissue
of the Pericycle.

Non-pitted Paren-
chyma of the Peri-
cycle

Fibro-vascular
Bundle

Usually two layers
of palisade paren-

chyma_ developed
on the upper leaf
surface. The re-

mainder of the me-

sophyll consists of

spongy parenchy-
a (Fig. 28).

Two circular canals
present. These con-
sist of an _ outer
layer of thick
walled cells and an
inner epithelial
layer of thin walled
cells.

Consists of a single
layer of thin-walled
elliptical cells that
bound the me-
sophyll on the in-
side and separate it
from the pericycle
(Fig. 31).

Always present :
found in two
masses, one bor-

dering each phloem
area (Fig. 31).

Fills between the
two divisions of the
bundle and projects
on each side but
more plentifully on
the dorsal (Fig.
a1).

Phloem and xylem
consist of an aver-
age of 7 rows of
cells. Medullary
rays found between
the rows.

MorRPHOLOGY AND BIOLOGY OF INSECT GALLS

No distinction be-
tween palisade cells

and spongy par-
enchyma.
Irregular; varying

in form and size,
on account of the
absence of the layer
of strengthening
cells.

Endodermis seldom
distinguishable.
Cells irregular in
form and size. No
distinct boundary
between mesophyll
and pericycle.

Nearly always
present.

More irregular in
form and __ size.
Larger and thicker
walled than in nor-
mal.

Phloem and xylem
less developed than
in normal. The
cells are often
larger and thicker
walled. Medullary
rays are absent.

Cecidomyia impatientis O.S,

Host Impatiens biflora Walt.
A spherical, polythalamous gall attached to the host plant by a

tapering stalk. Produced by the deformity of a flower bud.
Dimensions :—Diameter at right angles to stalk axis 6 mm.

319

The same as the
preceding in the
fungus, but the cells
are very much
elongated ina plane
perpendicular to
the midrib and
parallel to the epi-
dermis.

Resemble the nor-
mal type in shape
and are the same in
number, but are
considerably larger
and the strength-
ening layer con-
sists of very irreg-
ularly shaped cells.

Only a few cells
differentiated and
these are irregular
in shape and much
enlarged (Fig. 30).

Found in from 2-4
layers around the
inner side of the
endodermis. It
comprises the great-
er part of the peri-
cycle. The cells
contain protoplas-
mic material (Fig.
30).

Developed only be-
tween the bundles
and ina single row
along the edge of
the bast (Fig. 30).

Phloem and xylem
better developed
than in the normal,
the latter is more

irregular. The me-
dullary rays are
absent.

320 TRANSACTIONS OF THE CANADIAN INSTITUTE [VOL. Ix

There are three well differentiated zones. Immediately inside the
small celled epidermis is a mass of large thin-walled cells irregularly ar-
ranged. The walls of these cells are seldom straight but usually present
a wavy outline. They diminish in size progressively, passing in from the
periphery of the gall until they merge into quite a well defined nutritive
zone. This tissue is illustrated in Fig. 32. In this zone the cells are
very much smaller and are arranged in rows radiating out from the larval
chamber. Vascular strands pass irregularly throughout the gall. There
is no indication of a protective layer separating the two inner zones.

Cecidomyia majalis Bass.
Quercus rubra L.
Quercus coccinea Muench.

A flat pouch-like gall on the under side of the leaf. The opening
which extends the entire length of the gall is on the upper side. It is
produced by a folding of the blade of the leaf; this fold is parallel with
and very close to the midrib or a main vein.

Dimensions :—Along the line of its attachment to the leaf, diameter
4-7 mm.

The gall has been formed in this case by a folding of the blade of the
leaf. The resulting type recalls the pouch-like form usually associated
with the Eriophyide or more rarely the Aphidide.

The part of the blade included in the fold has not a well defined
palisade and spongy parenchyma, the mesophyll being practically uni-
form throughout. The cells of this region are much larger than those
of the normal leaf and are placed together without intervening air spaces.
At the apex of the fold the leaf blade is much thicker than at. any other
part of it (Fig. 27).

The epidermis that lines the interior of the fold seems to remain
intact throughout all the developmental stages of the larva.

Hosts

Cecidomyia ocellaris O.S.
Host Acer rubrum L.

A circular ridge on the under side of the leaf and a slight convexity
on the upper surface constitute the chief part of this gall. In the depres-
sion the larva rests covered with a viscid fluid secretion. The effect of
the stimulation extending out from this centre is shown in the different
coloured concentric rings produced in the leaf blade. These colourschange
in the course of development of the gall through various shades of red,
green or yellow.

The slight depression in the leaf blade that constitutes this gall has
been produced in the following way. The part of the leaf blade that
forms the bottom of the depression has remained practically normal,

1912] MORPHOLOGY AND BIOLOGY oF INSECT GALLS 321

but around this the blade of the leaf has become about five times as thick
as the normal organ. A circular ridge is thus formed that produces a
saucer-shaped hollow in the leaf blade. This can be clearly seen in Fig.
33. The cells that form this ridge are placed at right angles to the blade
of the leaf, in nearly the position of the palisade parenchyma. There
has been very little increase in the number of the cells, the accretion in
thickness of the blade being due principally to the lengthening of the
cells already present in the normal leaf.

_ Wherever a vein occurs in the gall, the cells are arranged in less
regular rows and the individual cells are much larger and not nearly so
elongated in outline. Intercellular spaces are not found in any part of
the gall tissue. The feeding habits of the larve are such as do not
necessitate the destruction of the epidermis lining the gall.

Cecidomyia pellex O.S.
Host Fraxinus americana L.

This gall is formed by a swelling of the blade of a leaflet on each
side of the midrib, the cortex of which also undergoes a proliferation that
merges insensibly with the mesophyll. Since the production of tissue
is unequal on the two sides of the leaf, a folding of the blade occurs with
the upper surface on the inside and the midrib at the apex. The
depression thus formed constitutes the larval chamber.

Dimensions :—Along the line of che midrib 10-25 mm.

The greater part of the gall mass is produced from the mesophyll
of the leaflet but a small part originates from the cortex of the midrib.
The epidermal cells have not been stimulated to division. It is possible
to determine the origin of the cellular elements from the circumstances
that in the gall, as in the normal leaf, the veins mark the boundary be-
tween the palisade and the spongy parenchyma. About two-thirds has
originated from the spongy parenchyma and the remainder from the
palisade layer. The greater amount of tissue thus produced from the
lower surface causes the folding of the leaflet with the sinus of the fold
above.

The cells produced from the spongy parenchyma are several times
larger than the normal. They constitute a tissue in which intercellular
air spaces are entirely lacking. On the other hand, the cells that owe
their origin to the palisade parenchyma, while larger than the normal
cells, are considerably smaller than those originated from the spongy
parenchyma. The latter with their epidermal covering constitute the
nutritive layer of the gall. Near the surface of this tissue, where the
larve are feeding, the cells have initiated divisions; here too they show
signs of collapsing.

322 TRANSACTIONS OF THE CANADIAN INSTITUTE [VOL. IX

Cecidomyia triticoides Walsh.

“On Salix cordata Muhl. A polythalamous woody gall .70-1.23
inch long and .30-.37 inch in diameter, bearing a remote resemblance to
a head of wheat with the kernels elongated, naked, pointed and very
protuberant, its general outline oval or elongate-oval, and formed by the
swelling of a twig to 2 or 3 times its former diameter, the swelled portion
being very much contracted longitudinally, so as to bring each kernel-
like bud nearly or quite into contact with the base of the one that pre-
cedes it in the same row, the whole number being arranged in four irregu-
lar rows.’’—Walsh.

The larval chambers in this gall are placed usually along the line of
the fibro-vascular bundles of the stem, and wherever a chamber is situ-
ated the vascular tissues are not developed.

An examination of a young stage of this gall shows that nearly the
whole of the pith and cortex of the stem consists of a well defined aeri-
ferous tissue. It is absent in only a few cell layers that surround the
larval chambers. Represented in Figs 34, 35, 36. At this stage there is
a well differentiated protective sheath, of about five cells in depth,
around each larval cavity. The cells of this layer have uniformly thick-
ened walls and are arranged in concentric rows around the larval chamber.
Each cell of this zone contains either a crystal aggregate or a well defined
single crystal of calcium oxalate. Inside of this protective sheath is a
nutritive layer which consists of about six rows of thin-walled cells.
The cells of this zone have the same tangential arrangement as those of
the protective sheath. Many of them are empty, this being especially
the case in the innermost row. Likewise, many are commencing to
collapse on account of the withdrawal of their contents. These zones
are represented in Fig. 38.

A section of a gall at a much more advanced stage of development
presents several important differences. The aeriferous tissue is very
much compressed in the pith and somewhat in the cortex. The cell walls
of the protective zone are now much thicker, and a well defined crystal
of calcium oxalate completely fills the lumen of each cell (Fig. 37).

Weidel* has recorded a phenomenon similar to this occurring in
the gall Andricus corticis Hart.

“Oft ist das ganze an sich schon grosse Zellumen durch einen ein-
zigen Kristall ausgefiillt, dem anscheinend so ansehnliche Zellulose-
massen spaterhin waren sie verholzt, aufgelagert worden sind, dass diese
die Wand des BehAlters erreicht haben und mit ihr verwachsen sind.”

My observations differ in one respect from Weidel’s, namely, there
is no ensheathing mass of cellulose around the crystals found in the gall
dealt with here. In deciding this point tests were made at different
stages with Schulze’s solution.

1gta} MorPHOLOGY AND BIOLOGY OF INSECT GALLS 323

There is a cambium layer lying just outside the protective zone in
the later stages. The nutritive layer consists of a mass of collapsed cells
that stain deeply with hematoxylin. These layers are shown in Fig. 37.

Lasioptera cornt Felt.
Feats Cornus alternifolia L.
Cornus paniculata L’Her.

This gall appears on the upper side of the leaf as a circular elevation
but does not project on the under side.

The colour is entirely green when young but becomes surrounded by
a circle of red at later stages.

In anatomical structure the tissues that compose this gall are the
same as those in the normal leaf.

The lower epidermis and the row of mesophyll cells immediately
in contact with it remain in the normal position. The upper epidermis
and the remainder of the mesophyll become arched and thus separate
from the lower epidermis and the part of the mesophyll that adheres to
it in the manner shown in Fig. 40. In the space thus formed the larve
are found.

Lastoptera impatientifolia Felt.
Impatiens biflora Walt.

Hosts mpatiens pallida Nutt.

A monothalamous gall, projecting chiefly from the under side of the
leaf. It consists of an elongated, spindle-shaped swelling of the midrib.
Dimensions :—Longer diameter 8-12 mm.
Shorter diameter 3-4.5 mm.

Practically all the abnormal tissue in this case is produced from the
cortex of the midrib of the leaf. The stimulation has extended out only
a very short distance into the adjoining mesophyll. The general mass
of gall tissue consists of large cells with a few small intercellular air
spaces. The epidermal cells are larger than those of the normal epi-
dermis, their increased length being particularly noticeable. The features
are shown in Fig. 41.

A nutritive layer is not differentiated.

Neolasioptera perfoliaia Felt.
Host Eupatorium perfoliatum L.

A spindle-shaped swelling of the stem forming a monothalamous
gall. It varies in size in proportion to the diameter of the stem or branch
from which it originates.

It may be stated as an almost invariable rule, that when a gall and
the plant organ from which it originates have a common epidermis the
cell walls of that epidermis are thicker in the area covering the gall than

324 TRANSACTIONS OF THE CANADIAN INSTITUTE [VOL. Ix

elsewhere. But this gall is an exception to the rule. While the outer
walls of the epidermal cells are considerably thickened in the normal
they are much less so in the gall. Also the two layers of collenchyma
cells underlying the epidermis in the normal stem are absent.

The increase in size of the stem where the gall is situated is due
principally to increased cell division in the cortex, since the epidermis
produces only two additional layers. The cells produced in the cortex
are larger than the normal, but the most peculiar feature to be noted is
the mode in which division has taken place and the relative arrangement
of the products of division. The location of this tissue is illustrated in
Fig. 23. The method of cell division is clearly the same in this species
as in the two Lepidopterous types Stagmatophora ceanothiella and Gnort-
moschema asterella. The clusters contain from 2 to 6 members produced
from a single cell. The dividing walls are straight, and at the stage ex-
amined had the greatly elongated nuclei in close contact with them.
These nuclei were seldom exactly opposite but usually diagonally across
from one another. These characteristics are represented in Fig. 23.
Schtirhoff*! has described the mode of division in callus, contrary
to the views in vogue, he states that the nuclei divide mitotically only.
There is good reason to believe that the phenomena observed here corre-
spond very closely to those given in his account.

Near the inner edge of the cortex, glands are regularly spaced around
the stem. This is a rather remarkable fact as they do not occur normally
in this part of the stem. Indeed it was only after a careful search that
they were located in the transition region between root and stem. The
search was extended to other species with the result that they were
found in Eupatoria purpureum L. in the roots, the cortex and the re-
productive axis, but in EZ. urticefolium Reichard as in E. perfoliatum L.
only at the base of the stem.

Rhabdophaga batatas Walsh.

“On Salix humilis Marsh. A polythalamous gall of very variable
shape and size, pale green when young, the colour of the bark when mature,
growing on twigs .06-.19 inch in diameter and always some distance from
the tip of the twig. Sometimes it resembles a small kidney-potato
pierced lengthways by a twig, and has then most generally a smooth
polished surface studded with a few buds, one or two of which occasion-
ally give birth to a shoot, and it then reaches 1.35 inch in length and
.6 inch in diameter. Sometimes it resembles a young apple pierced
lengthways by a twig and attains a diameter of .3 inch.’ —Walsh.“

In this gall the larval cells are situated in the pith of the host plant,
just inside the line of the fibro-vascular bundles. The epidermis has a
much thicker cuticle than that borne by a normal stem of corresponding

1912] MORPHOLOGY AND BIOLOGY OF INSECT GALLS 325

age. The cortex is approximately four times as thick as the cortex of
the normal stem. This is due principally to the increased size of the
cells. The cells of the nutritive layer are very similar to those of the
surrounding tissues but a well marked protective zone defines its outer
limits. This is clearly shown in Fig. 25.

The cells of the protective zone present a characteristic very rare
in Dipterous galls, although frequently found in the Cynipid galls,
namely, the walls of the cells are not uniformly thickened but are much
heavier on the side next the nutritive zone. This unequal sclerification
is illustrated in Fig. 26. Crystals of calcium oxalate, that were so char-
acteristic a feature of this zone in C. triticoides Walsh, seem to be en-
tirely absent in this gall.

Rhabdophaga strobiloides Walsh.
Host Salix cordata Muhl.

“The galls are very uniform in size and form, usually top-shaped,
some inclining to spherical, a little oblate below and prolate above, and
as the female oviposits but one egg in the terminal bud of the willow
shoot, the galls are terminal and monothalamous.

“The gall is a rather tightly and regularly arranged mass of from
70 to 80 aborted leaves, representing perhaps about I m. of the leafage
of a normal branch.

“The average measurement of 200 galls was 12 mm. X15 mm., and
the length of the deformed part of the branch included in the gall around
which the aborted leaves were packed was 6 mm.’’—Brodie.®

The leaves that constitute the principal mass of this gall do not
take any part in supplying the larva with food. The tissue that has this

function is composed of a mass of small, thin-walled cells. It terminates
the stem axis and the larva is in immediate contact with it (Fig. 24).
This tissue which really furnishes a nutritive layer seems to originate
from a cambium-like tissue at the base of the mass of cells.

An important factor in the production of this gall is the practical
cessation of growth of the bud axis.

The aborted leaves that compose the gall exhibit very slight ana-
tomical aberrations.

Eurosta solidagints Fitch.

Host Solidago canadensis L.

A monothalamous gall produced by the swelling of the stem of the
host plant. Very rarely it is found on a branch of the flowering panicle.
A separate gall is almost perfectly spherical in form but occasionally two
are produced together forming a common gall, prolate-spheroidal in shape.

Dimensions:—Average diameter of fifteen galls, 23 mm.

326 TRANSACTIONS OF THE CANADIAN INSTITUTE [VOL. Ix

The cells that compose the principal mass of this gall are slightly
smaller than those of the normal pith but in other respects they resemble
them very closely. The irregularity in position of the fibrovascular
bundles and their imperfect development are well marked features.
Yet a sufficient water supply is ensured to the tissues by vascular strands
that are given off from the bundles. These strands extend in a radial
direction towards the centre of the gall.

The cortex is considerably thicker than that present in the normal
stem. This is due in part to the greater number of cell layers, but also
to an increased size.

The glands that are present in the normal stem of Solidago cana-
densis L. occupy certain fixed positions. One gland is present in the
cortex outside each bundle and one inside in the region of the pith. The
glands found in the cortex of the gall are very much enlarged and have
not their characteristically regular arrangement. In the gall pith they
are abundant throughout (Fig. 42), but decidedly more plentiful in the
vicinity of the fibro-vascular strands. This is the most striking example
of gland proliferation found in the galls studied.

The tissues that supply the larva with food are not differentiated
into a nutritive zone.

Summary.

The galls produced by this order of insects vary very much in their
degree of complexity. Some forms such as Cecidomyia ocellaris O.S. are
as simple in structure as an Acarina, ‘‘Dimple’’, gall; other species as
Rhabdophaga batatas Walsh present all the specialized anatomical char-
acteristics of a Cynipid gall.

The abundant production of glands in tissue ve stimulation is
very clearly exemplified in Eurosta solidaginis Fitch. At first sight it
appeared as if glands were not present in the host of Neolasioptera per-
foliata Felt, but they were located at the base of the stem and in other
species of Eupatoria.

The unequal thickening of the tangential walls of the sclerenchyma
protective layer in Rhabdophaga batatas Walsh is a very unusual pheno-
menon in this group.

Cecidomyia triticoides O.S. is the only gall of this group in which a
well defined crystal layer was found. In it each cell lumen is entirely
filled with a single crystal of calcium oxalate.

The production of the aeriferous tissue, that occupies practically
the entire pith in the gall Cecidomyia triticoides Walsh, is one of the
most interesting phenomena exhibited in this group. The nature of this
will be discussed in the biological section of the paper.

The collapsing of the nutritive zone after the cell contents are with-
drawn is well exemplified in Cecidomyia triticoides Walsh (Fig. 37).

1912] MorPHOLOGY AND BIOLOGY OF INSECT GALLS 327

The unusual type of cell division in the cortex of the hosts infected
by certain Lepidopterous forms, e.g. Stagmatophora ceanothiella Cosens
and Gnorimoschema galle@asterella Kellicott and described in that group,
is also found in the Dipterous gal! Neolasioptera perfoliata Felt (Fig. 23).
It was not found in any Cynipid form.

A comparison of a leaf of Abies balsamea (L.) Mill infected by
Cecidomyia balsamicola Lintner with one from a witches’ broom produced
on the same host by Acidium elatinum (Melampsora Caryophyllacearum)
brings out a number of interesting points. These are given in the tabu-
lated form following the description of the species C. balsamicola Lintner.

ORDER HYMENOPTERA.

Following Marlatt’s Revision of the Nematinz of North America,
U.S. Dept. of Agriculture, Washington (1896), the species considered
in this paper are comprised in the Subfamily Nematinz, Family Ten-
thredinide. They are included in two genera, Pontania and Euura.
The species referred to are:—

Euura S. gemma Walsh.

Euura S. ovum Walsh.

*Fuura (undescribed).

Pontania pisum Walsh.

Pontania pomum Walsh.

Pontania desmodioides Walsh.

Pontania hyalina Norton.

*Pontamia (undescribed).
*Gall on Salix lucida (undescribed).

Gall on Salix humilis (undescribed).

*Specimens of the first three producers marked (undescribed) were
- sent to S. A. Rohwer of the Smithsonian Institution.

I have been successful in rearing the producers of all of the unde-
scribed forms except in the case of the one on S. humilis Marsh. This was
accomplished in the following manner. The galls were collected at the
‘time of the falling of the leaves of the host plants and were placed on
earth in breeding jars which were kept under conditions of heat and
moisture approximating as closely as possible to that of the natural
habitat. Pupation took place at a distance of about a couple of inches
below the surface of the soil and the adults emerged the following spring.
The dates of emergence were :—

Pontania (undescribed), April 14 to April 24.

Euura (undescribed), May 2 to May 6.

Gall on S. lucida (undescribed), April 20 to April 22.

“While this paper was in press, Rohwer‘ published the description of these producers.

Following the order above the names assigned are,—Euura serissim@ Rohwer,
Pontania crassicornis Rohwer, P. lucide Rohwer.

328 TRANSACTIONS OF THE CANADIAN INSTITUTE [VOL. 1x

The close restriction of sawfly gall producers to definite species of
Salix can be illustrated by means of the forms mentioned in this paper.
The host plants of the species are:—

Euura S. gemma Walsh
Pontania desmodioides Walsh
Pontania (undescribed)
found on Salix humilis Marsh.
Pontania hyalina Norton
on S. alba L.
Pontania pomum Walsh
on S. cordata Muhl.
Euura (undescribed)
on S. serissima Fernald.
Gall (undescribed)
on S. lucida Muhl.
Pontania pisum Walsh
on S. discolor Muhl.
In this locality I have not found the above species on any other host
than that mentioned. When the type of gall is higher it would seem to
be axiomatic that the relations between the host plant and producer
would be more intimate than when the gall does not stand so high in
the scale and as a consequence the restriction to one host plant would be
a necessity. Yet the galls produced by the Cynipide are often found
on two or three different hosts; as, for example, Amphibolips inanis O.S.
on both Quercus rubra L. and Q. coccinea Muench, Dryophanta palustris
O.S. on Quercus rubra L. and Q. coccinea Muench. Aulax nabah Brodie
on Prenanthes alba L. and P. altissima L.

Euura S. gemma Walsh.

“On Salix humilis. The lateral bud of a twig enlarged so as to be
twice or thrice as long, wide and thick as the natural bud before it begins
to expand in the spring; its external surface otherwise entirely unchanged
both in texture and colour. Internally, instead of the normal downy
embryo leaves, it contains early in the autumn a homogeneous grass-
green fleshy matter, which is afterwards gradually consumed by the
larva, leaving nothing at last but a mere shell partly filled with excre-
ment. The gall is monothalamous, sometimes one only on a twig, some-
times two or three or more at irregular intervals, very rarely as many
as three or four formed out of three or four consecutive buds.

Length .17 to .36 inch

Breadth .10 to .17 inch.—Walsh.#

The anatomy of this gall presents little differentiation of tissue. A
cross section shows that the entire mass of the gall consists of small

1912] MORPHOLOGY AND BIOLOGY OF INSECT GALLS 329

thin-walled cells, shown in Fig. 68. The bud scales surrounding this
group of cells resemble those of the normal bud except that the cuticle
of the epidermis is abnormally thickened.

Euura S. ovum Walsh.

“On Salix cordata. An oval or roundish, sessile, monothalamous
swelling, .30 to .50 inch long, placed lengthways on the side of small
twigs, green wherever it is smooth, but mostly covered with shallow
longitudinal cracks and irregular rough scales which are pale opaque
brown. Its internal substance fleshy in the summer like that of an apple,
but with transverse internal fibres. When ripe in the autumn filled with
reddish-brown spongy matter, with close-set transverse internal fissures
at right angles to the axis of the twig. On cutting down to the twig at

“any time a longitudinal slit about .20 inch long becomes plainly visible.’’-—
Walsh.“

As already noted the host of this gall in this locality is Salix humilis,
it remains to be determined whether there are two distinct species of
producers or one species with two hosts. Walsh’s description of the gall
on Salix cordata corresponds to the form occurring here on S. humilis.

The ovipositor of the producer has in this case made a longitudinal
cut in the stem. A transverse section at the place where the gall is
located shows that this wound extends in from the epidermis to the boun-
dary of the pith. The activity of the young tissues, abnormally stimu-
lated, soon fill this fissure with a mass of small, angular parenchyma.
The rapid division of these cells forces the exposed edges of the cortex
and central cylinder apart so as to form a wedge-shaped opening which
is filled up with the gall mass (Fig. 71). It should be stated that the
newly formed cells originate mainly from the division of a cambium

_bordering the pith at the bottom of the fissure. But other tissues also
respond to the stimulation initiated by the ovipositor of the insect.
Thus a section of the stem at a short distance from the gall shows that
the outlying cambium has become abnormally active and has produced
a layer of bast nearly one-third thicker than that found in the normal
stem. Likewise the activity of a cork-cambium layer has thrown off a
strongly cuticularized epidermis present in the earlier developmental stages.

Undescribed Sawfly Gall (Euura N.S.) on Salix serissima Fernald.

Fig. 1.—A nearly mature gall attached to a leaf of the host plant.

330 TRANSACTIONS OF THE CANADIAN INSTITUTE [VOL. 1x

This gall is produced by the abnormal swelling of the petiole of the
leaf. The leaves infected are those borne on the branchlets from which
spring the pistillate catkins. In the majority of cases, the leaf thac
bears the gall is the one from the axil of which the peduncle of the catkin
arises. The swelling is so close to the branchlet that after the leaves
have fallen, the gall appears to have originated from it. This misleading
appearance is due to the petiole of the leaf breaking just above the gall.
The galls are cone-shaped with che apex towards the blade of the leaf.
They are marked deeply by three or four grooves that meet at the tip.

Dimensions :—Height of gall 7-8 mm.; diameter at base 6-7 mm.

The anatomy of this gall presents a very compact tissue, owing to
the cells being placed close together without intervening air spaces.
The very much thickened cuticle of the epidermis is the greatest departure
from the normal tissue. Of the three bundles of the normal petiole two
are lacerated by the ovipositor of the insect, as shown in Figs. 69, 70. In
the mature gall the halves of these two are found in four widely separated
regions (Fig. 69), owing to the abundant production of tissue between
them. Indeed practically all the abnormal tissue is produced from the
undifferentiated cells stimulated by the cutting of the bundles.

Pontania pisum Walsh.

“On Salix discolor. A subspherical, pea-like, hollow, pale yellowish-
green gall, always growing on the under side of the leaf and almost always
from one of the side veins (in one case from the midrib), and attached
to the leaf by only a minute portion of its surface; 0.18 to 0.28 inch in
diameter and a few miniature, only 0.08 inch in diameter. Almost in-
variably there is but one gall to the leaf, but on four leaves there were
two, and occasionally two are confluent. Surface in some smooth and
even without pubescence; in others a little shriveled, generally studded in
the medium-sized ones with four to twelve small, robustly conical nipples,
which in the larger ones have burst into a scabrous brown scar. Only in
three out of sixty-two was there any rosy cheek as in P. pomum. The
point of attachment is marked on the upper side of the leaf by a brown
sub-hemispherical depression.’’-—Walsh.“

Walsh is incorrect in supposing that this gall originates from a
midrib or vein. A section shows that it is clearly a product of the meso-
phyll and is attached to that part of the leaf. The side vein, near which
it is always placed, is cut by the ovipositor, however, and vascular
strands pass out from it into the gall body.

The mature gall consists of a peripheral layer of thin-walled cells,
irregular in outline surrounding a central cavity (Fig. 81). This tissue
is clearly derived from the mesophyll and epidermis of the leaf, but a
stage was not secured young enough to show the relative amounts

1912] MORPHOLOGY AND BIOLOGY oF INSECT GALLS 331

produced from each. The epidermis bears numerous lenticels, organs
which Kiister** mentions as occurring on the gall produced by Pontania
salicts.

At the point of attachment of the gall the blade of the leaf is strength-
ened by several rows of cells derived from the upper epidermis and the
palisade parenchyma, as shown in Fig. 81. These cells seem to have
remained unmodified in any way, since their arrangement in rows is still
clear in fairly old stages of the gall. Consequently they differ very
markedly from the irregularly arranged cells of the main part of the gall
body.

Pontania pomum Walsh.

“On Salix cordata (and very rarely on S. discolor). A smooth,
fleshy, sessile, globular or slightly oval, monothalamous gall, resembling
a miniature apple, .30 to .55 inch in diameter, growing on one side of the
midrib of a leaf, and extending to its edge or sometimes a little beyond it.
The principal part of the gall generally projects from the under side of
the leaf, and only about one-sixth of its volume from the upper side,
although very rarely it is atmost equally bisected by the plane of the leaf.
Scarcely ever more than one gall on a leaf and very rarely two of them,
more or less confluent so as to seem like one kidney-shaped gall. Ex-
ternal colour greenish-yellow, generally with a rosy cheek like an apple
especially on the upper surface and often with many dark little dots on
its surface.’-—Walsh.#

The ovipositor of the producer of this gall has been thrust laterally
through the midrib of the leaf into the mesophyll. The wound has com-
pletely severed the bundle of the midrib, as seen in Fig. 76.

The full-grown gall presents an epidermis with a very thick cuticle.
The remainder of the gall consists of a complex of thin-walled cells
arranged so as to constitute a typical aeriferous tissue (Fig. 77). A
similar arrangement of cells is not found in the normal leaf, the mesophyll
of which consists of a fairly compact tissue. The vascular strands growing
_ out from the wounded bundle form a complete ring around the gall,
situated about half way between the epidermis and the centre.

I was successful in obtaining this gall at such an early stage that
the egg membrane was still unbroken (Fig. 76). This phase shows that
the epidermis, the palisade and the spongy parenchyma mutually take
part in the gall production. Counting along a line passing through the
centre, four of the cell layers are seen to have arisen from the lower
epidermis and six from the upper, eight from the palisade and fifteen
from the spongy parenchyma of the leaf. Hence it is noteworthy that
the new tissues are not the product of a cambium but have been contri-
buted to by every morphological region of the leaf. The cells that are

332 TRANSACTIONS OF THE CANADIAN INSTITUTE [VOL. Ix

produced at this stage are in rows generally in exact alignment with the
cells from which they have arisen. They thus do not have the arrange-
ment of the aeriferous tissue of later stages to which they give rise.
The cuticle, so marked a feature of the older stages of the epidermis, is
exceedingly thin. The epidermis bears trichomes springing from the
bottoms of deep pits (Fig. 76). This condition has arisen through the
circumstance that the primary epidermal cells from which hairs have
grown out have not experienced the periclinal divisions participated in
by their fellows and so have been left far below the general surface as
shown in the text fig. below.

Fig. 2.—Hairs originating from pits in the epidermis of P. pomum Walsh.

Pontania desmodioides Walsh.

“On Salix humilis. A smooth, flattish, fleshy, sessile, yellowish-
green monothalamous gall of a semicircular outline, the chord of the
semicircle adjoining the midrib of a leaf; its general shape like the seed
of a Desmodium or like the so-called ‘‘quarter’’ of an orange, the thin
inside edge of the ‘“‘quarter’’ closely hugging the midrib of the leaf, and
the robust outer surface not biangulated but rounded off. No rosy cheek.
The volume of the gall is generally about equally divided between the
upper and lower sides of the leaf but sometimes the lower portion is
rather the larger. Usually there is but a single gall on a single leaf, but
occasionally there are two of them, either on the same side or on opposite
sides of the midrib.’””-—Length .23 to .50 inch Walsh.“

When mature this gall shows in cross section a cavity surrounded
by a peripheral layer of little differentiated tissue. The epidermis has
given rise to a very thick cuticle that is not present in the normal leaf.
The bundle of the midrib has been injured only slightly by the ovipositor
of the producer. The vascular strands given off from it almost encircle
the gall along a line half way in from the epidermis.

A stage of the gall so young that the larva was unhatched shows
the gall tissue to have been produced by cell division in the upper epi-
dermis, the spongy parenchyma and the palisade parenchyma of the
normal leaf (Fig. 80). At the thickest part of the gall, when it is in this
stage, the upper epidermis has produced four layers of cells, the spongy
and palisade parenchyma seven layers each. The lower epidermis has
not divided as yet, and probably takes no part in the production of the

1912] MorPHOLOGY AND BIOLOGY OF INSECT GALLS 333

gall. The abnormal cells from the palisade parenchyma show clearly
their origin by their arrangement in rows at right angles to the surface
of the leaf. The cells produced by the spongy parenchyma, on the
other hand, are not regularly placed but include air spaces. The result
is that the abnormal tissue in this case also resembles the normal tissue
from which it is derived.

This stage of the gall shows that the cavity present in the mature
gall has arisen between the tissue produced by the spongy and that
derived from the palisade parenchyma of the normal leaf.

Pontania hyalina Norton.

“Fleshy galls occurring in two parallel rows, one on either side of the
midrib, sometimes touching but not originating from the latter, and
rarely extending to the edge of the leaf; sometimes as many as twenty
on a single leaf; in other cases confined to a row on one side of the leaf
or occasionally occurring singly; shape irregular elongate-ovate, pro-
jecting equally on both surfaces of the leaf; length 7 to 10 mm.; the
abortive ones smaller. Colour on upper side more or less brownish red;
beneath white, with slight purplish tinge.”—Marlatt.”

The anatomy of this gall presents scarcely any differentiation of
tissue. When mature it consists of a mass of thin-walled chlorophyll-
bearing cells, the innermost of which are arranged in rows almost at
right angles to the blade of the leaf, as seen in Fig. 75. Cells are so much
alike that they afford no clue as to their origin.

Again I was able to obtain material so young that the larva was still
confined within the egg membrane (Figs. 73, 74). It shows that the
spongy parenchyma, the palisade parenchyma and the epidermis of the
normal leaf were jointly concerned in the production of the abnormal
tissue. The spongy parenchyma has contributed nearly half of the
entire mass, the epidermes three layers each, and the row of cells
immediately overlying the lower epidermis three layers. The remainder
has been derived from the palisade parenchyma.

Undescribed Sawfly Gall (Pontania N.S.) on Salix humilis Marsh.

Fig. 3.—Two galls attached on opposite sides of the midrib.

334 TRANSACTIONS OF THE CANADIAN INSTITUTE [VOL. Ix

This is a monothalamous gall found on the leaves of Salix humilis.

It is spherical in shape and in that feature resembles P. pomum,
but in other respects it differs very markedly. It extends from the side
of the midrib almost out to the margin of the leaf and is divided into
two hemispheres by the leaf blade. In consequence the gall protrudes
nearly equally from each leaf surface. Usually there are two or three
galls on a leaf. When two are present they come in contact with the mid-
rib at the same place but on opposite sides, as illustrated in Fig. 79. In
a few cases four and even five galls were found on one leaf. The galls
are pubescent but not as densely as the under surface of the leaf.

Dimensions:—Average diameter I cm.

The mesophyll of the leaf and the upper epidermis are mutually
concerned in the production of this gall. In one, sufficiently immature
to show the relative amount of tissue arising from each source, it was
found that the upper epidermis had produced two cell layers, while the
lower had not responded to stimulation; and that the palisade and spongy
parenchyma had each produced one-half of the remaining mass. The
hollow in the gall, present from the earliest stages, has been formed
between the tissue arising from the palisade and the spongy parenchyma
respectively.

When only one gall originates from the midrib at any point, the
vascular bundle is cut approximately half through (Fig. 78). But more
frequently two galls are located opposite one another, one on each side
of the midrib, in which case the two incisions meet and completely sever
the bundle, as seen in Fig. 79.

Vascular strands pass almost completely around the gall, along a
line half way between the epidermis and the gall cavity. These strands
originate from the midrib in the neighborhood of the injury and pass in
opposite directions.

Undescribed Sawfly Gall on S. lucida Muhl.

Fig. 4.—Two galls produced on the same leaf of the host.

This gall consists of an enlargement of either the petiole or midrib
of S. lucida. Neither of these organs bears, as a rule, more than one gall

1912] MorRPHOLOGY AND BIOLOGY oF INSECT GALLS 335

at a time, but occasionally the petiole of a leaf carries two or even three
and the midrib in rare instances two.

The midrib galls are fairly regularly elliptical in outline with the
shorter diameter across the leaf. The swellings in most cases are nearly
equally divided between the upper and the lower leaf surfaces. The
petiole galls vary from spherical to ovoid in shape. In the latter case
the smaller end of the gall is towards the apex of the leaf.

Dimensions of the gall:—Longer diameter 6-12 mm.; shorter dia-
meter 3-7 mm.

The very marked proliferation of tissue in this gall is not accompanied
by a differentiation that presents many points of interest. The cells are
larger than those of the normal leaf and the nuclei are correspondingly
larger. The bundle is cut nearly through by the ovipositor (Fig. 82).
The free ends of the bundle thus stimulated grow out until in some cases
they almost surround the gall. This elongation is produced in part by
the increased diameter of the vessels but also by the production of new
cellular elements.

The pith, exposed by the cutting of the bundle, produces almost
all the abnormal tissue (Figs. 83, 84), but the cortex contributes some.
The cells are arranged in curved lines that pass across from one elon-
gated end of the bundle to the other. Between these rows are many air
spaces which are elongated in the direction of the lines of cells (Fig. 84).

Undescribed Sawfly Gall on Salix humilis Marsh.

Fig. 5.—Leaf of the host with attached gall.

This is a monothalamous gall produced by the abnormal swelling
of the leaf petiole of S. humilis. It is conoidal in shape with a long taper-
ing apex which is towards the blade of the leaf. As it is situated at the
base of the petiole the uniform enlargement of that organ is often pre-
vented by the axillary bud. This causes the gall to project to a greater
extent on the outside of the petiole and produces an irregularity in the
outline of the gall. The surface is quite glabrous in spite of the fact that
the epidermis of the leaf is decidedly pubescent.

Dimensions:—Length of gall 6-9 mm.; width 3-4 mm.

Nearly the entire mass of this gall originates from the vascular
bundle of the petiole which has been stimulated to activity by the in-
sect’s ovipositor. The small thin-walled cells of the gall substance

336 TRANSACTIONS OF THE CANADIAN INSTITUTE [VOL. Ix

spring from a cambium layer produced in the pith of the bundle near
the ovipositor wound. The cells arising from this tissue force the severed
ends of the bundle apart until the vascular elements form only a narrow
line of cells between the gall proper and the cortex of the petiole; it is
shown at this stage in Fig. 85. This cortex is not materially thickened
but shows signs of stimulation in that there appears a small amount of
aeriferous tissue located near the place of entrance of the ovipositor. This
tissue is shown on each side of the wound in Fig. 85. This tissue was
not found in the normal cortex of the petiole. The cuticle is very much
thickened.
Summary.

Great proliferation of tissue with little differentiation is a common
characteristic of all sawfly galls.

All the leaf tissues of the genus Salix appear to be susceptible to
stimulation by sawfly producers.

The pith of the bundle produces practically the whole mass of the
gall when the place of origin is the petiole or the midrib of the leaf. In
the case of a stem gall a layer of cells bordering the pith produces the
chief proliferation.

When the gall originates from the mesophyll of the leaf the bundle
of the midrib produces relatively only a very small part of the total
gall mass.

Of the remaining tissues of the leaf the upper epidermis responds
more readily to stimulation than the lower and the spongy parenchyma
more actively than the palisade parenchyma.

In some cases the abnormal tissues exhibit the characteristics of
the normal from which they have originated. The cells produced to
form a solid base of attachment for the gall Pontania pisum Walsh never
lose their arrangement in vertical rows, and the cells that originate from
the same tissue in P. desmodioides Walsh are also in vertical series (Figs
80, 81).

Adler! secured specimens of Nematus vallisnierti in which the larva
was still within the egg. I have been equally fortunate with the species
Pontania pomum Walsh, Pontania hyalina Norton and Pontania desmo-
dioides Walsh. At this early developmental stage considerable prolifer-
ation of tissue had already occurred. Adler even reports that the gall
was nearly full grown. My experience has been that the larve are
invariably found feeding unless the material is secured almost as soon
as the galls are visible to the unaided eye. At this time little swelling
of the leaf tissues is apparent, but a discoloration of the leaf enables the
wound of the ovipositor to be detected. Owing to cell proliferation pre-
ceding the emergence of the larva, Adler concluded that the immediate

1912 MORPHOLOGY AND BIOLOGY OF INSECT GALLS 7
9 33

cause of cell activity, productive of sawfly galls, is the wound caused by
the act of ovipositing. But there is a slight possibility that secretions or
excretions from the developing larva may be active through the egg
membrane.

The protective sclerenchyma sheath of the more advanced types of
galls is absent in this group, and the only protective device appears to
be the cuticularizing of the epidermis and the presence of tannin in the
cells. The cuticle has also a more important function in preventing the
desiccation of the underlying thin-walled tissues of the gall.

The possible significance of the aeriferous tissue found in Pontania
pomum Walsh will be discussed later in this paper.

Lenticels on galls seem to occur very rarely. They were found in
this group only in the one species, Pontania pisum Walsh, a leaf gall.

The restriction of the various species in many cases to single hosts
seems noteworthy when the minor specific differences between the
members of the Salicacez are considered.

A series of the undescribed species of Euura on Salix serissima
Fernald furnished undoubted examples of cell proliferation produced
by the excrement of the larval producer (Fig. 72). This fact is discussed
in the biological section of the paper.

LOCALIZATION OF TANNIN-BEARING TISSUE IN SAWFLY GALLS.

Kiistenmacher*® has discussed the question of tannin in certain
Cynipid galls and Cook” has detected it in different stages of a number
of galls, but no attempt has been made up to the present to work out its
distribution in the family Tenthredinide.

Pontania pomum Walsh.

Tannin-containing cells are abundant in the epidermis of this gall.
They are found also in the ‘‘Aeriferous tissue,’’ but are not so numerous
there. They are plentiful in the vascular strands, but can scarcely be
demonstrated in the tissue next the larva.

In the normal leaf of Salix cordata Muhl. these cells are abundant,
especially so in the vascular tissue and the epidermis.

Undescribed Pontania Gall on S. humilis Marsh.

Tannin-containing cells are very plentiful in the epidermis and in
six or seven rows of cells that immediately underlie that tissue. They
are also present in the vascular strands and in the tissue next the larva.

In the normal leaf of S. humilis Marsh these cells are not present in
the epidermis of the midrib but are found in the bundle of the midrib
especially in the bast portion.

338 TRANSACTIONS OF THE CANADIAN INSTITUTE [VOL. Ix

Pontania hyalina Norton.
Tannin cells are found abundantly in the epidermis and in the gall
tissue generally, except the cells on which the larva is feeding.
In the normal leaf of S. alba L. on which this gall is found, these
cells are not present in the epidermis of the midrib but are plentiful in
the wood and bast of the bundle.

Pontania desmodioides Walsh.

Tannin cells are plentiful in the epidermis and in the underlying
tissue, but gradually diminish in number in the tissues nearer the larva.

This gall also is found on S. humilis Marsh.

Undescribed gall on petiole of Salix lucida Muhl.

Tannin cells are found practically all through the tissues of the gall,
but tannin is most plentiful in the epidermis and in the petiole that is
involved in the gall swelling.

Tannin cells are found throughout the normal petiole except in the
parenchyma tissue immediately underlying the epidermis.

Conclusions concerning Tannin-bearing Tissue.

(1) Tannin is more plentiful in gall tissue than in the normal tissue
from which it originates.

(2) In gall tissues it is most abundant in the epidermis and the bast.

(3) It is more abundant in the older than the younger stages of galls.

(4) It does not appear to function as food for the larve as the
tannin cells are less abundant in the tissue on which the larve feed.

(5) As tannin is always plentiful in the gall epidermis it may serve
for protection by rendering the gall tissues unpalatable.

Technique used in Testing for Tannin. j

The test substance used was a saturated solution of ammonium
chloride saturated with ammonium molybdate.

Razor sections of the galls were used for testing.

NOTES ON OVIPOSITING BY SAWFLY GALL PRODUCERS.

Pontania hyalina Norton.

The leaves of Salix alba L. are folded in the bud with the under
surfaces towards the outside. The ovipositing takes place before the
leaf selected has separated from the others in the same bud. As a conse-
quence of this the ovipositor is inserted from the ventral surface of the
leaf (Fig. 74).

May 27th, 1911.—On this date a producer was observed ovipositing
in young leaves, but other leaves on the same stem lower down bore galls
that were almost full size.

June 3rd and 4th.—On these dates producers were seen ovipositing.

June 18th.—Producers ovipositing.

1912] MorPHOLOGY AND BIOLOGY OF INSECT GALLS 339

August 11th.—Galls were found in which the ovipositing could have
taken place only a few hours before. The ovipositing in this species must
continue over a period of at least two months.

Pontania pomum Walsh.
Pontania desmodioides Walsh.

These producers begin to oviposit at about the same date as the
above species. The period of ovipositing must comprise a comparatively
short space of time as the galls of these species are all at about the same
stage of development on the same date.

The galls produced respectively on Salix cordata Muhl. and Salix
humilis Marsh. by these producers are not found near the tips of the
young stems, but the galls on Salix alba L. produced by Pontamia hyalina
Norton are found on leaves along the whole length of the young stems.
This difference in the location of the galls is caused by the period of ovi-
positing being much longer in Pontania hyalina Norton than in the other
two species.

The first effect of ovipositing by Pontania pomum Walsh, visible to
the unaided eye, is a dark red colour produced in the leaf blade surround-
ing the spot where the ovipositor has entered. This colour is also visible
for a short distance along the midrib of the leaf. When the gall is opened
at this stage the egg of the producer can be found with the aid of a lens.
It is elliptical in outline and of pearly lustre. The membrane is trans-
lucent and the egg contents can be distinguished through it.

ORDER HYMENOPTERA.

Whenever possible the specific names have been selected from the
monographs by Wm. Beutenmuller,*!* that are now being issued from
the American Museum of Natural History, New York. These publica-
tions give full synonymy and bibliography of the different species.

The following species are here described :—

Fam. Cynipide.

Holcaspis globulus Fitch.

Holcaspis bassetti Gillette.

Philonix erinacei Beut.

Philonix hirta Bassett.

Philonix nigra Gillette.

Amphibolips confluens Harris.

Amphibolips inants O.S.

Dryophanta palustris O.S.

Andricus imbricarie Ashmead.

Andricus singularis Bassett.

340 TRANSACTIONS OF THE CANADIAN INSTITUTE [VOL, IX

Andricus piger Bassett.

Andricus petiolicola Bassett.

Andricus (undescribed).

Rhodites multispinosus Gillette.

Rhodites lenticularis Bassett.

Rhodites ignotus O.S.

Rhodites bicolor Harr.

Rhodites gracilis Ashm.

Rhodites nebulosus Bassett.

Cynips? constricta Stebbins.

Solenozopheria vaccinit Ashm.

Aulacidea nabali Brodie.

Neuroterus majalis Bassett.

Aylax glechome Linné (referred to the section on Cytology).

Holcaspis globulus Fitch.
Host Quercus alba L.

A monothalamous, spherical gall produced at the nodes of the stem
of the host.

It occurs singly or in groups of from two to four. Thecolour is yellow-
ish-green usually with a reddish tinge. When mature the oval larval
chamber is free from the remainder of the gall. The aperture of exit of
the producer is placed at the end of this larval cell.

Dimensions :—Average diameter 13 mm.

When this gall is so young that it is still soft, it has the following
anatomical characteristics. The larval chamber is in organic continuity
with the remainder of the gall. Beneath the small celled epidermis are
four or five layers of cells with their long axes parallel to the periphery
of the gall. Inside this tissue is the more typical part of the parenchyma
zone. Here the cells are in radial rows forming a fairly compact tissue
with only a few small air spaces. Their radial walls are more elongated
the nearer they are to the larval chamber. Inside of the parenchyma
zone is a poorly defined cambium tissue that passes gradually into a
crystal layer. Each cell of this zone contains a large crystal mass. A
second cambium tissue, in this case well defined, bounds the crystal
layer on the inside. From this cambium the nutritive layer is produced.
This consists of cells, almost square in outline, arranged in radial rows
(Fig. 65).

The protective zone is differentiated only in the later stages of de-
velopment. It is found, however, when the gall is mature, forming the
entire wall of the free larval chamber and extending a short distance
beyond it. Its cells are of the usual sclerenchyma type with uniformly
thickened, laminated walls perforated by branched simple pores.

1912] MORPHOLOGY AND BIOLOGY OF INSECT GALLS 341

Holcaspis bassetti Gillette.
Host Quercus macrocarpa Michx.

A monothalamous gall occurring singly or in clusters around the
stems of the host. When grouped the galls often cover completely 4 to 5
inches of the stem.

When the gall is not deformed by crowding, it is irregularly circular
in outline at the base, gradually tapering to a distinct point that is re-
curved in most cases. The gall is attached to the host by a small stalk
at the centre of the base. Colour green, often tinged with pink when
young; becoming brown when more mature. The larval chamber re-
sembles closely that found in the former species in being oval and free
at maturity, but it differs in being placed nearer the base of the gall and
in tapering to a point at the end nearer the twig.

Dimensions :—Diameter at base, average, 16 mm.

Except in a few details the anatomical structure of this gall is the
same as that found in the species just described. In this species the
outer part of the parenchyma zone is composed of cells almost square
in outline, but towards the larval chamber the cells become more elongated
and arranged in distinctly radial lines. Rays of from one to three cells
in width pass in radial lines throughout this zone. The cells composing
them are much smaller than the ordinary cells of the zone. The cells of
the nutritive layer are much more elongated radially than those of H.
globulus Fitch (Figs. 58,65). The cambial layers and the crystal-bearing
tissue hold the same relative positions as in the preceding species. The
relation of the crystal layer to the nutritive zone is shown in Fig. 58.
The protective sheath in the mature gall extends out almost to the epi-
dermis. Except in its distribution it cannot be distinguished from the
corresponding zone in H. globulus Fitch.

Philonix erinacei Beut.
Host Quercus alba L.

A polythalamous gall springing usually from the midrib but rarely
from a principal vein of the leaf. It originates from the under or occa-
sionally the upper surface of the leaf.

The gall is spherical or ellipsoidal and slightly flattened on the sur-
face in contact with the leaf. The point of attachment is narrow and
elongated in the direction of the vein. The epidermis of the gall is divided
up into numerous facets, each of which is drawn out at the centre into a
trichome structure that becomes more spiny as the gall approaches
maturity. Thecolourof thesurface of the gall is yellowish with occasional
red tints. The trichomes vary in shade from pink to red.

Dimensions :—Longer diameter 10-15 mm.; shorter diameter
5-10 mm.

342 TRANSACTIONS OF THE CANADIAN INSTITUTE [VOL. IX

In the earliest stage examined the gall was 2 mm. in diameter.
At this time none of the cell walls are sclerenchymatous and the nutri-
tive zone is only about four narrow cells in width. Outside of this layer
is a part of the parenchyma zone in which each cell contains a large
crystal mass.

At a stage in which the gall is full grown but still soft, all the zones
are differentiated. The epidermis is thrown into folds and is covered
with a heavy cuticle (Fig. 64). This is absent in the sinuses of the folds
and on the epidermis covering the spines. The parenchyma zone is
gradually converted into a protective tissue of porous sclerenchyma.
The thicker deposit is usually on the walls of the cells nearer the periphery
of the gall. Along the outside of the nutritive zone and throughout the
protective layer generally are lines of small cells almost square in outline.
The walls of these cells are very thick and the lumen of each is filled with
a single crystal or a mass of crystals. In galls that had become hard all
the cells of the parenchyma zone were found to have sclerified. The
sclerification is partially complete in Fig. 64.

The nutritive layer of this gall differs very little in appearance from
the parenchyma zone. Its cells do not contain the rich protoplasmic
contents common to the nutritive zones of typical Cynipid galls.

Philonix hirta Bassett.
Host Quercus macrocarpa Michx.

A monothalamous, spherical gall originating from a principal vein
of the leaf. Found somewhat irregularly spaced along the vein and about
equally distributed between the upper and lower surfaces of the leaves.

The epidermis has the same faceted appearance found in the pre-
ceding species, but in this form the trichomes are represented only by
short points. Colour greenish yellow. When the leaves become tinted in
the autumn the galls assume a reddish brown colour.

Dimensions:—Diameter 2-3 mm.

The anatomical structure of this gall differs from P. erinacet Beut.
only in the distribution and nature of the protective zone. This tissue
is limited to a layer 3 to 4 cells in thickness, just outside the nutritive
zone. The sclerifying deposits are limited almost entirely to the outside
tangential walls of these cells and gradually entirely fill them. As a
result of this the pores pass completely across the cells in the older
stages. The small square crystal-bearing cells are, in this species, just
outside the regular protective sheath.

Philonix nigra Gillette.
Host Quercus alba L.

A monothalamous gall attached to the principal veins on the under

side of the leaf.

1912] MORPHOLOGY AND BIOLOGY OF INSECT GALLS 343

This species is spherical in form and has an epidermis covered with
a short dense pubescence that gives a felty appearance to the exterior of
the gall. A fibrous mass of cells surrounds the centrally placed larval
chamber. Colour gray turning darker when dry. Individuals of this
species are so numerous that the ground, under the trees infested by
them, is often covered thickly with galls.

Dimensions :—Average diameter 8 mm.

Outside the nutritive zone is a wide crystal layer, each cell of which
is completely filled with a crystal mass. The sclerenchyma of the pro-
tective zone is formed in a very unusual manner. The sides of contiguous
cells are thickened in such a way that there is an almost spherical deposit
at the points where the cells are in contact.

Radiating out from the protective layer are long narrow cells which
form the minor part of the parenchyma zone. The remainder of this
zone consists of irregularly elliptical, thin-walled cells. The epidermis
is covered with a dense growth of trichomes with thick laminated and
sclerified walls.

Amphibolips confluens Harris.
Host Quercus coccinea Muench.

A monothalamous gall attached to the petiole or midrib of the leaf.
The midrib is never continued beyond the point of origin of the gall.

Globular to prolate spheroidal in shape and invariably terminating
in a minute point. The thick walled larval cell at the centre of the gall
is surrounded by a sponge-like mass of fibres that is at first white but
becomes dark brown when the gall is dry. At a very early stage of de-
velopment the epidermis of the gall is pubescent but later it becomes
smooth. The colour is at first green but this changes to a lustrous light
brown when the gall is old.

Dimensions :—Average diameter 40 mm.

(a) Stage in which the gall is 2 mm. in diameter.

Almost the entire gall consists of a compact tissue, which is composed
of small uniform cells. Lines of narrow elongated cells, however, pass
- in a radial direction throughout this tissue. These cells do not extend
into the gall cavity nor out to the epidermis, they traverse about two-
thirds of the gall radius. As they approach the epidermis the lines curve
around and run parallel to its surface. Spiral vessels are in some cases
differentiated in these rays and the elements are more numerous near
the point of attachment of the gall.

(b) Older stage 9 mm. in diameter.

The gall wall can now be divided roughly into three sections. That
part lying next the larval cell resembles closely the compact tissue de-
scribed in the preceding stage, except that immediately adjoining the

344 TRANSACTIONS OF THE CANADIAN INSTITUTE [VOL. Ix

cavity a typical nutritive layer has been formed by the elongation of the
cells in a radial direction. In the centre zone the lines of cells containing
the vessels are much more apparent at this stage, since the intervening
tissue has become loose and skeleton-like. The cells composing it are
long, very narrow and frequently branched. In many cases a branch is
attached to the main cell without the formation of an intersecting par-
tition between the two. The outside zone of the three is composed of
somewhat elliptical cells. These form a fairly firm tissue constituting
the rind of the gall.

(c) Mature stage.

The protective zone is now the most characteristic feature of the
anatomical structure. The part of the protective sheath adjoining the
larval cavity consists of a few layers of elliptical cells arranged in tan-
gential rows. The sclerenchymatous deposits on the outside walls of
these cells are much heavier than those on the inside. Further out the
protective cells are formed in radial rows and their walls are uniformly
thickened. This protective strengthening of the cell walls extends even
into the loosely arranged filament-like cells, some of which are heavily
sclerified.

Amphibolips inanis O.S.
Hosts Quercus coccinea Muench.
Quercus rubra L.

Resembles the preceding species in external appearance and in its
attachment to the midrib or the petiole of the leaf.

In shape it is more nearly spherical than A. confluens Harr. and it
has a much thinner rind than is found in that species. The epidermis
of the gall, which is at first green with dark spots, becomes light brown
with darker patches at a later stage. The larval cell in this case is held
in position by a number of fine radiating fibres.

Dimensions :—Average diameter 35 mm.

In the earlier stages the anatomical structure of this gall is practi-
cally the same as A. confluens Harr. The vascular strands surrounded
by elongated cells are present, but as the gall becomes older the connect-
ing tissue from between the strands disappears.

In the mature gall the protective zone is very apparent. It consists
of 8 to 10 rows of comparatively small elliptical cells. The walls of these
cells are uniformly thickened, constituting a porous sclerenchyma.

Dryophanta palustris O.S.
Quercus rubra L.
Hosts Orereus coccinea Muench.

A monothalamous gall produced singly or in groups of two or more
on the leaves of the host plant. It is spherical in form and extends almost

ee

1912] MorPHOLOGY AND BIOLOGY oF INSECT GALLS 345

equally on each side of the leaf. In the majority of cases the gall extends
out almost to the margin of the leaf and only the edge of the blade rims
its outer side. Rarely this gall is found originating from the peduncle
of the staminate catkin of the host.

The very young gall of this species is densely pubescent, while the
well-grown specimens are usually quite smooth. In galls collected when
the leaves are just beginning to unfold from the bud the larval cell and
the outer zones of the gall are united, but very soon a separation occurs
and the larval cell is left rolling freely around in the outer gall. Colour
of mature gall green with patches of red in some places.

An average of about three weeks elapses from the time of the open-
ing of the buds until the producers emerge from the galls. After another
week the galls are wrinkled, dried up and brown. About ten days before
the time of emergence of the producers the larval chambers were removed
from several galls and placed under dry conditions. While the time of
emergence of these producers was not appreciably changed, the insects
in almost every case had difficulty in freeing themselves from the larval
cells and one wing usually remained shrunken. It would appear that the
outer gall during the later stages of development functions only as a
moist chamber for the prevention of the desiccation of the larval cell.

The youngest galls examined were obtained from leaves that were
just breaking out of the bud. At this stage the larval chamber still has
organic connection with the remainder of the gall (Fig. 49). A well-
defined cambium zone, in which mitosis is taking place, divides the gall
wall into nearly equal parts. The parenchyma layer on the outside
extends from the cambium to the epidermis. It consists of small cells
that resemble closely those of the cambial zone. The inner half of the
gall, forming the nutritive layer, is composed of much larger cells ar-
ranged in rows radial to the larva. A canal passes from the outside into
the larval chamber. The epidermal lining of this canal is continuous
with that of the epidermis of the gall and is covered with the same class
of trichomes (Fig. 49). It gradually passes over into the innermost
layer of the nutritive zone.

In a very short time after the opening of the buds, the larval chamber
is severed from the remainder of the gall. The break occurs near the
outside of the cambium zone, and separation has commenced in Fig. 50.
At this stage the protective layer is not yet differentiated. Soon after
the separation occurs it is produced, however, and the four zones of a
typical Cynipid gall are complete.

The cells of the protective sheath are placed tangential to the larva.
There are two layers of these cells, both of which have one tangential
wall thicker than the other. In the outer row the thicker wall is towards

346 TRANSACTIONS OF THE CANADIAN INSTITUTE [VOL. Ix

the larval chamber, but in the inner row the reverse is the case. On the
outside of the protective zone are about two layers of round, loosely con-
nected parenchyma cells (Fig. 51). The canal mentioned in the early
stage is still visible, penetrating the outer wall of the gall and that of the
larval chamber. A layer of collapsed tissue is now clearly defined around
the inside of the nutritive zone (Fig. 51). The inner layer of the paren-
chyma zone is also showing this same tendency to collapse.

In the mature gall the nutritive zone is represented by only a narrow
layer of shrunken tissue (Fig. 52), the individual cells of which cannot be
distinguished. The inner layer of the parenchyma zone is now almost
completely collapsed and the cell walls of the whole zone are wrinkled.

Andricus imbricarie Ashmead.
Host Quercus coccinea Muench.

A globular gall issuing from the stem of the host plant. Several
galls are found near each other on the stem but they are never crowded.

It is usually monothalamous, but occasionally dithalamous forms
are found, the larval cells are closely connected with the remainder of
the gall. When the gall drops off its point of attachment is marked by
a small, elliptical, depressed area surrounded by thin scales of tissue.
These scales represent tissue forced aside by the emergence of the young
gall.

Dimensions :—Diameter 6-9 mm.

This species has the four zones well differentiated. The most
striking features of the anatomical structures are the following :—

The cells of the protective layer contain large crystal masses and
have their walls uniformly thickened. Radiating lines of cells pass out
from this protective zone (Fig. 48), through the parenchyma sheath and
end near the epidermis. These bands are composed of narrow, elongated
cells and are from 1 to 3 cells in width. These rows of cells contain a
great deal of starch and a substance that takes a very deep stain with
saffranin. Large cells of the parenchyma zone separate these bands of
cells from each other, as seen in Fig. 48.

Andricus singularis Bassett.
Host Quercus rubra L.

In the majority of cases this gall originates from the mesophyll of
the leaf blade but rarely it is found attached to the petiole. It is situated
near the margin of the blade of the leaf and projects about equally from
the upper and lower surface.

It is a monothalamous gall closely resembling in external form
Dryophanta palustris O.S., but its outer wall is much firmer and it does
not wither so quickly after the producer emerges. The ellipsoidal, larval
chamber is suspended at the centre of the gall by radiating bands of

1912] MORPHOLOGY AND BIOLOGY OF INSECT GALLS 347

tissue which pass inwards from the gall rind; this gives the species a
superficial resemblance to small specimens of Amphibolips inanis O.S.

Dimensions :—Diameter 10-15 mm.

The larval chamber in this species is suspended at the centre of the
gall by fine strands of tissue. These are composed of long, narrow, fila-
ment-like cells interspersed with spiral vessels. These fibres represent
the inner part of the parenchyma zone. The outer part of this zone
resembles closely that found in the gall produced by Dryophanta palus-
tris O.S. The cell walls of the epidermis are strongly thickened and this
is the case also in the underlying layer of cells of the parenchyma sheath.
The protective zone, when the gall is full grown, consists of two rows of
porous, laminated sclerenchyma cells. The outside tangential walls of
these cells are much more thickened than the inside walls. The cells of
the nutritive layer are unusually large and almost square in outline. By
the time the gall is nearly mature many of them have been emptied of
their contents and a wrinkling in the radial walls shows that the whole
tissue is collapsing (Fig. 59).

Andricus piger Bassett.
Host Quercus coccinea Muench.

A polythalamous gall produced by the swelling of the petiole or
midrib of the leaf. It is situated always near the distal end of the petiole
or the proximal end of the midrib.

It is an irregular, elongated structure, somewhat triangular in cross
section. When it originates from the midrib the projection is almost
entirely from the under surface of the leaf, the broad flattened part of
the midrib above rising very little above the general surface of the blade.
On the under surface of the leaf along each side of the gall is a row of
small openings. The larval cells are in two rows following the line of the
openings. The total number in the gall varies from 20 to 30.

Dimensions :—Length of longer diameter 20-25 mm.

A nearly mature specimen shows the following anatomical character-
istics. The four typical zones are well defined. Surrounding the nutri-
tive zone are three rows of cells that form the protective zone. The walls
of these cells are porous laminated and uniformly thickened. Outside of
the protective sheath is a zone of tissue of about the same width, each
cell of which contains a large crystal aggregate. These masses of crystals
alone distinguish this tissue from that of the parenchyma zone into which
it gradually passes by the crystal groups becoming less plentiful.

Connected with the openings mentioned in the macroscopic descrip-
tion are remarkably straight canals that extend in as far as the protective
sheath. At this point they are closed by cone-shaped plugs of scleren-
chyma (Figs. 43, 44), that extend out from the protective zones of the

348 TRANSACTIONS OF THE CANADIAN INSTITUTE [VOL. Ix

larval cells towards which the canals are passing. The cells of this tissue
are identical with those of the ordinary protective zones.

From analogy with Dryophanta palustris O.S. (Fig. 49), and with
other species of Andricus it would seem safe to infer that this canal opens
into the larval chamber at earlier stages in the development of this gall.
This also appears more likely to be the case since the protective zone
that blocks the way, is differentiated only in the later stages.

Andricus petiolicola Bassett.
Host Quercus alba L.

This gall is produced in the same manner as A. piger Bassett by the
swelling of the petiole or midrib. It is also located at the same place on
the leaf as that species.

It has an irregular, spherical shape drawn out at some place on its
surface into a short tapering projection. At the summit of this elongated
part of the gall is an opening surrounded by a dense ring of coarse, brown
trichomes. The larval cells are numerous and very variable in number.
They are arranged around the axis of the gall at about the same distance
from the epidermis.

Dimensions :—Diameter of the swollen basal part 10-12 mm.

In this species the protective layer is much thicker than in A. piger
Bassett, but the individual cells composing it are the same in both species.
The galls sectioned were nearly mature but the crystal layer of the former
species was not found.

In this species also there is a canal passing towards each larval
chamber (Fig. 46). These canals do not open directly to the outside
but into a main canal of larger bore that extends a considerable distance
into the mass of the gall (Figs. 45, 46). The branch canals are blocked
by the protective sheath as in the preceding species. All of the canals
are lined with a cuticularized epidermis, continuous with the gall epi-
dermis (Fig. 45). The lining of the main canal produces abundant tri-
chomes but these structures do not appear to be present in the tribu-
taries. A tubular outgrowth of the protective zone surrounds the main
canal. This sclerenchymatous sheath is separated from the canal by
several layers of parenchyma cells. Outside of this protective tube a
cork cambium is differentiated.

Andricus (Undescribed).
Host Quercus macrocarpa Michx.

The swelling of the midrib of the leaf produces this gall. It resembles
closely A. piger Bassett, but is always found within the blade of the leaf,
although close to its base in most cases.

The openings mentioned in the two preceding species are in this
case found on the surface of the gall which appears on the upper side of

1912] MORPHOLOGY AND BIOLOGY OF INSECT GALLS 349

the leaf. They correspond to the larval cells, varying from 3 to 7 in
number.

Dimensions :—Length parallel to axis of midrib 10-15 mm.

Although nearly mature specimens of this gall were sectioned, a
protective zone was not found.

In this species each larval chamber has a canal related to it. In
this respect it resembles A. piger Bassett. A section of the gall at a very
early stage of development shows that the canals open into the larval
chambers. When the gall becomes older, each canal is blocked by two
plugs of sclerenchyma. One of these occupies the same position relative
to the larval chamber as in the two preceding species; the other is formed
near the external opening. These masses of sclerenchyma are shown
in Fig. 47. Trichomes do not appear to be produced in the canals.

Rhodites multispinosus Gillette.
Host Rosa blanda Ait.

A globular to ovoid polythalamous gall produced by the swelling of
the stem or branches of the host plant. Since the larval cells are arranged
around the stem axis at about the same distance from the periphery of
the gall, the abnormal swelling completely encircles the stem.

The gall is reddish brown in colour and has its surface usually densely
covered with fairly stout prickles.

Dimensions :—Average diameter 25 mm.

The principal mass of this gall is formed from the cortex of the stem.
The larval cells are embedded in it and a common parenchyma zone is
thus formed. A well-marked protective tissue, composed of cells with
porous, sclerenchymatous walls, separates this parenchyma zone from
the nutritive tissue that lines each larval cell.

The response of the gall epidermis to stimulation is shown in the
production of the numerous prickles that are so marked a characteristic
of this gall. Since the stem of the host is usually unarmed this feature
appears the more remarkable.

Rhodites lenticularis Bass.
Host Rosa blanda Ait.

A monothalamous, lens-shaped, thin-walled gall produced in the
mesophyll of the leaf of the host. They sometimes occur singly but
usually several are located on one leaflet. They often are so crowded
that they lose their circular outlines.

This gall projects chiefly from the under side of the leaflet.

Dimensions:—Longer diameter 2-3 mm.; shorter diameter I-2 mm.

Since it is possible to trace a considerable part of the unaltered
mesophyll of the leaf along the upper surface of this gall, proliferation
must have commenced in the spongy parenchyma of the leaf. The

350 TRANSACTIONS OF THE CANADIAN INSTITUTE [VOL. Ix

normal epidermis of the leaf passes over the surface of the gall without
modification. On the upper surface of the leaf a protective layer of about
five cells in depth separates the normal part of the leaf from the gall
tissue. On the under surface a corresponding protective layer occurs at
a distance of three rows of cells below the epidermis. The cells of this
protective zone have uniformly thickened sclerenchymatous walls. The
general structure of the gall is shown in Fig. 63. Inside this layer a
cambial tissue is differentiated, from which the cells of the nutritive zone
are produced directly. The nutritive cells are rectangular in outline and
arranged in radial lines, presenting very much the same appearance as
the cambium from which they have originated.

Rhodites bicolor Harr.
Rosa blanda Ait.
Hosts{ po, carolina L.

A monothalamous, spherical, hollow gall with a wall 1 to 2 mm. in
thickness.

They originate singly or several close together from the upper sur-
face of the leaf.

The gall bears numerous stiff prickles that average about the same
length as the diameter of the gall. Colour green with red tints, turning
brown at maturity.

Dimensions :—Average diameter 11.5 mm.

The anatomical structure of this gall presents very little differenti-
ation of tissue. The parenchyma zone consists of large irregularly shaped
cells. This tissue passes into the nutritive layer with little change in the
shape or size of the cells. The protective zone is entirely absent.

Rhodites ignotus O.S.
Host Rosa blanda Ait.

A polythalamous or occasionally monothalamous gall attached to
the under side of the leaves by a small extent of surface. These galls
are generally found clustered together and often deform the entire leaf.

Dimensions :—Average longer diameter II mm.; average shorter
diameter 3-5 mm.

While somewhat variable, the shape approximates usually to an
irregular oblate-spheroid. At the apex of the gall is a shallow depression
containing a small scale-like patch of tissue. The epidermis is glaucous
and light brown in colour.

The anatomical structure of this species presents the rare feature of
two protective layers. These are each of about five cells in thickness in
the full-grown gall. One of them is found in the usual position separating
the parenchyma and the nutritive zones. The other is situated in the

1912] MORPHOLOGY AND BIOLOGY oF INSECT GALLS 351

parenchyma just beneath the small-celled epidermis. This outside pro-
tective sheath gradually passes into the parenchyma zone by the con-
stituent cell walls becoming thinner. The large size of the cells in the
parenchyma layer marks them out from the rounder and smaller cells of
the nutritive zone.

Below the depressed area, mentioned in the macroscopic description,
is a small patch of sclerenchymatous cells. In position and character
these cells appear to be homologous to the groups of cells that block the
canals in different species of Andricus. Only the mature stage of this
gall was examined, but in all probability the depression at the top is the
remains of a canal that connected the gall cavity with the outside in the
early stages of development. A part of the normal epidermis of the leaf
was held fast by the closing of this canal, and when the gall was forced
out beyond the leaf tissues a small patch of the epidermis of the leaf was
carried out on it. This persists in the later stages of development as the
scale of tissue in the depression.

Rhodites gracths Ashm.
Host Rosa blanda Ait.

A thin-walled, monothalamous gall produced from the mesophyll of
the under surface of the leaf of the host. Occurs singly or in clusters on
the leaflets.

It is irregularly spherical with a broadened top, in the centre of
which is the same shallow depression and scale-like patch found in R.
ignotus O.S. Numerous ridges radiate out from the point of attachment
of the gall, pass up its sides and project as short blunt tubercles around
the top.

Dimensions :—Diameter 5-6 mm.

This species resembles closely R. bicolor Harr. in anatomical struc-
ture. It presents little differentiation of tissue. The protective sheath
is not present, and the parenchyma and nutritive zones are marked out
from each other only by the cells of the latter being slightly smaller and
_ more circular in outline. The observations on the preceding species con-
cerning the depression at the summit of the gall and the discussion of
them also apply to this species.

Rhodites nebulosus Bass.
Host Rosa blanda Ait.

This species, as the preceding, is monothalamous and thin-walled. It
also originates from the mesophyll of the leaf of the host. It occurs
usually in dense clusters deforming the entire leaflet.

The gall is spherical in form, bearing at the summit the depressed
area and scale-like patch characteristic of the two preceding species.

352 TRANSACTIONS OF THE CANADIAN INSTITUTE [VOL. Ix

The surface of the gall is smooth or covered with short weak spines.
Colour green, tinted strongly with red.

Dimensions :—Diameter 5-6 mm.

This gall resembles closely the preceding species in anatomical
structure. The cells of the nutritive and parenchyma layers differ in
much the same way and to the same extent. Further, the protective
zone is again absent. The explanation given in the two preceding forms,
to account for the scale in the depression at the summit of the galls, is
applicable also in this case.

Cynips? constricia (Stebbins).
Host Quercus coccinea Muench.

A monothalamous gall originating from the midrib or a principal
vein of the leaf. Its origin from a vein is shown in Fig. 53. It is usually
found on the under side of the leaf but occurs occasionally on the upper
side.

This gall has the form of a sphere surmounted by a short cylindrical
neck, which is slightly constricted at the base. The general form is
shown in Fig. 54. A very small portion of its surface attaches it to the
leaf. The epidermis on the main body of the gall is smooth, shiny and
green in colour. The neck is red at the tip.

Dimensions :—Diameter of spherical part 2.5-3.5 mm.

At an immature stage of the gall the parenchyma zone in the
spherical part consists of a mass of cells that gradually decrease in size
from the epidermis to the inner limit of the layer. At the epidermis
the cells are nearly circular in outline but become square or rectangular
in proportion to their proximity to the centre.

Bounding this zone on the inside is a crystal layer of about three
cells in thickness, each cell containing a large crystal mass. Around the
inside of this tissue is a nutritive zone, the cells of which are regularly
rectangular.

At the top of the main part of the gall is a well-defined cambium
tissue which produces the cylindrical projection that caps the spherical
portion (Fig. 54). The anatomical structure of this part shows clearly
that it functions as an outer nutritive zone. Its walls are thin and the
cell contents take the same stain as those in the nutritive zone surround-
ing the larva. Large starch grains are also scattered throughout the
cells. This zone is separated from the cambium tissue in the later de-
velopmental stages by a protective layer of typical porous sclerenchyma.
These cells are filled with protoplasmic material, and the system of canals
between the individual cells is very complete and clearly defined. This
feature is very important since the nourishment from the outlying nutri-
tive zone has to pass through this tissue to reach the larva.

1912] MorPHOLOGY AND BIOLOGY OF INSECT GALLS 353

Solenozopheria vaccinit Ashmead.
Vaccinium pennsylvanicum Lam.
Hosts hes
Vaccinium canadense Kalm.

A polythalamous gall originating from the lower part of the stem of
the host plant.

In the majority of cases this gall is reniform in shape but rarely it
is irregularly spherical. The surface is depressed where it is attached
to the stem, which is almost invariably bent at that point. Thecolouris
green, often with red tints turning to brown as the gall becomes older.

Dimensions :—Longer diameter 10-30 mm.

At an early stage, while the tissues are still soft, the anatomical
structure of this gall presents practically no differentiation. It consists
of a mass of dense tissue, the cells of which are small and placed very
close together. The small-celled epidermis is covered with an exceed-
ingly heavy cuticle. At regular intervals small papilla occur on the
epidermis which seem to secrete a glandular material from small open-
ings at their tips.

When the gall is mature all the cells, except a few layers below the
epidermis, have sclerified walls. The thickenings are decidedly heavier
on one wall than on the opposite.

Aulacidea nabali Brodie.
Heck ad cute alba L.
Prenanthes altissima L.

A polythalamous gall originating from the stem or the main root of
the host plant. It occurs at or near the base of the stem, usually just
below the surface of the ground but in some cases it is situated some
distance above the ground.

The single galls are irregularly spherical, but these are generally
- clustered in such a way as to form roughly cylindrical masses. In some
cases these completely surround the stem, but in others they only partly
encircle it.

Dimensions :—Diameter of single gall 5-10 mm.

The cambium of the stem stimulated to unusual activity produces
the abnormal tissues in this case (Fig. 66). Along the line of contact of
the gall with the normal stem, the cambium produces wood and bast,
but in abnormally large amounts, as can be seen in Fig. 66. In the gall
tissue proper, in place of wood, radial lines of nucleated thin-walled cells
occur. A few rows of vessels are interspersed among these cells. The
stimulated cambium produces these parenchyma cells also on the side
where the bast would normally occur. In the gall tissue on the outside
of the line of the cambium, small patches of vessels are found. These
have arisen from clumps of cells detached from the original cambium.

354 TRANSACTIONS OF THE CANADIAN INSTITUTE [VOL. Ix

Associated with these isolated masses of vessels, often occurs a small
amount of bast that appears normal. When the detached cambium is
curved, wood is almost invariably produced on the inside of the curve and
bast on the outside, giving rise in some cases to almost perfect concentric
bundles.

The club-shaped cells of the nutritive zone do not follow the general
rule and radiate out from the larval cell, but are oriented with their long
axes atright angles to the cambium. The nuclei of the cells in this zone
are abnormally large and often present good examples of amitosis (Text
Fig. 6).

The normal cortex passes over the gall with little alteration during
the early stages of development, but later a cork cambium is differenti-
ated that throws off the cortex and covers the gall with its characteristic
corky layer.

Neuroterus majalis Bassett.
Host Quercus alba L.

A polythalamous gall originating in the mesophyll of the leaf and
divided into two nearly equal parts by the blade. The galls are found
usually in contact with the side of the midrib and extending out to the
margin of the leaf.

This gall is characterized by a flat, irregular shape and a finely granu-
lar epidermis. It is translucent and of a light green colour until the pro-
ducers emerge when it becomes light brown and opaque.

The apertures of exit of the mature insects seem to occur invariably
on the upper surface of the gall.

Dimensions :—Diameter parallel to leaf blade 12-24 mm.; diameter
at right angles to leaf blade 7-9 mm.

Only the mature gall was examined. At this stage the nutritive
zone consists merely of a narrow line of collapsed tissue (Fig. 67). From
two to three rows of cells constitute a protective layer. The tangential
walls of these sclerified cells are unequally thickened, the heavier deposit
being on the wall nearer the larval chamber. The parenchyma zone
consists of large thin-walled cells, the majority of which are empty and
devoid of nuclei. A small-celled epidermis continuous with that on the
normal leaf passes over the gall.

Summary.

All the galls in this group have three tissue zones developed and
only very seldom is the fourth absent. The three always present are the
epidermal, the parenchyma or tannin and the nutritive. The paren-
chyma zone, as shown by Cook’ is subject to a great amount of varia-
tion. The fourth, not always present, is the protective or sclerenchyma
zone.

1912] MORPHOLOGY AND BIOLOGY OF INSECT GALLS 355

Even in one genus there may be considerable variation in the degree
of development of the protective zone. It is entirely absent in Rhodites
gracilis Ashm. and R. bicolor Harr., but two distinct layers are found in
R. ignotus O.S.

In several species of the genus Andricus canals were found passing
from the exterior towards the larval chambers. In the early develop-
mental stages these opened into the gall cavity, but later were blocked by
outgrowths of sclerenchyma from the protective zone. They were located
in the species Andricus piger Bassett, A. petiolicola Bassett and Andricus
N.S. (Figs 43-47).

A canal similar to those in the Andricus genus was found also in
Dryophanta palustris O.S. In this species the plug of sclerenchyma is
not developed (Fig. 49).

An epidermal scale was found in the bottom of a depression at the
apex of the galls produced by certain species of Rhodites. Below each
scale a small mass of sclerenchyma is differentiated. These structures
seem to be homologous to the canals in the genus Andricus. They are
present in the following species: Rhodites ignotus O.S., R. gracilis Ashm.
and R. nebulosus Bassett.

The gall Solenozopheria vaccinii Ashmead has the sclerified tangen-
tial walls of its protective zone much thicker on one side than on the
opposite. This is very unusual in stem galls, although a common feature
in leaf galls.

The collapsing of the cells of the nutritive zone after the withdrawal
of the contents is exemplified in almost any gall studied. It is, however,
particularly noticeable in Dryophanta palustris O.S. (Fig. 52).

Empty cells were found throughout the nutritive zones in the later
stages of nearly all the galls examined. Good examples of this pheno-

_ menon are furnished by Andricus singularis Bassett and Aylax glechome

Linné.
The separation of the tissues so as to produce a free larval chamber
gall is shown in the species Holcaspis globulus Fitch and H. bassetti

Gillette; also in Dryophanta palustris O.S. (Fig. 50). In the last species,

as Cook*’ has shown, the separation of the larval chamber takes place at
a very early developmental stage.

Mitotic phenomena were observed in the cambium and near it in the
adjoining parenchyma zone of Dryophanta palustris O.S. The number
of chromosomes remains as in the normal. Good examples of amitosis
were located in the nutritive tissues of Aylax glechome Linné, and
Aulacidea nabali Brodie (Text Fig. 6).

The parenchyma zone of Amphibolips confluens Harris furnishes an
example of a tissue consisting of long filamentous cells from which

356 TRANSACTIONS OF THE CANADIAN INSTITUTE [VOL. Ix

branches are given off without the formation of intercepting walls. It

seems to represent an exaggerated form of the spongy parenchyma.
Proliferation of glandular tissue is shown in Aulacidea nabali Brodie.
Cynips? constricta Stebbins furnishes an example of an outer accessory

nutritive zone that clearly assists in supplying the larva with nourishment

(Fig. 54).
NOTES ON THE PROTECTIVE ZONE.

This zone is typical for the Cynipid galls, but as already stated it is
differentiated in certain Dipterous forms, such as Rhabdophaga batatas
Walsh (Figs. 25, 26) and Cecidomyia triticoides Walsh (Figs. 37, 38), and
also in the Hemipterous gall Pachypsylla celtidis-mamma Riley (Fig. 15).

In the Cynipide it usually bounds the nutritive zone on the outside,
but it does not invariably occupy that location. When two layers are
present the inner occupies that position, but the outer is situated nearer
the periphery of the gall.

The term, ‘‘protective,’’ has been applied to this tissue without a
very clear idea as to what it protects from. The common notion appears
to be that it forms an inner line of defence against parasites and small
animals other than insects. The latter class of enemies appears to inter-
fere very seldom with galls. Cook*® mentions one example—he found
birds tearing open the galls of Pemphigus vagabundus Walsh. Very few
examples of such cases have come under my notice. Galls of Holcaspis
bassetit Gillette are occasionally opened by woodpeckers, and the larve
of Eurosta solidaginis Fitch are sometimes taken from the galls by field
mice. Chipmunks will also tear open the galls of Pemphigus rhois Walsh
to get at the inhabitants. Not only are galls seldom attacked by such
animals but a sclerenchymatous tissue would be a very poor defensive
device against them.

Adler! has advanced the idea that this zone protects against insects
that are parasitic on the producer-larva. This appears very unlikely
since the parasites oviposit at a comparatively early stage, and the scleren-
chyma is differentiated relatively late in the development of the gall.
The same writer cites the large size of the gall and the thickened epidermis
as other protective devices against parasites. The same argument is
applicable in this case; the gall is not large nor is the epidermis abnormally
thick at the time the parasites are ovipositing. Were Adler correct the
gall Amphibolips confluens Harris should be almost immune against
parasites, as it is large, has a thick epidermis and a well-developed pro-
tective sheath. In spite of all these apparent advantages this gall has
a heavy casualty list owing to parasitism. During last season hundreds
of this species were opened and on an average about 75% were found to

'g12] MORPHOLOGY AND BIOLOGY OF INSECT GALLS 357

e parasitized. In some cases a tree would not yield a single perfect
roducer, although a couple of dozen galls were examined.

It seems safe to conclude that if this zone has ever functioned as a
eans of defence against parasites, it is no longer operative. Apparently
he only protective function that can be ascribed to this tissue is the pre-
ention of injury to the producer by desiccation during its later larval
nd pupal stages of development. A thick or cuticularized epidermis
ould also afford protection in the same manner.

Concerning the form of the elements comprising this zone, Weidel*
as recently made some interesting observations. He makes the follow-
ng too sweeping statement in his summary,—

“Auch das gallentragende Organ der Mutterpflanze hat einem

influss auf die Gestaltung der Elemente in der Galle, denn die blatt-
iirtigen Gallen fiihren in der Schutzschicht einseitig verdickte, die
ibrigen allseitig gleichmassig verdickte Zellen.”’
That this can be accepted only as a general rule, and at least requires
urther study, is indicated by the fact that our American galls furnish
undoubted exceptions. Thus the gall produced on the stem of Vaccinium
bennsyluanicum Lam. by Solenozopheria vaccinit Ashmead has cells that
have a much thicker deposit of sclerenchyma on one tangential wall than
on the other. In some cases practically the entire cell lumen is filled with
sclerenchyma and the deposit has grown entirely from one side of the
cell. Also a number of leaf galls have their protective zones composed
sntirely of cells with uniformly thickened walls. The following species
‘urnish examples of this: Amphibolips inanis O.S., Rhodites lent'cularis
Bass. and Neuroterus majalis Bassett. The statement quoted is true,
10wever, in the majority of cases and is important as indicating a possible
*ffect of environmental conditions on the elements composing the gall.

CYTOLOGY OF GALLS.

Cell division in the Cynipid galls was not found to present any un-
isual phenomena. In the cambial layer of Dryophanta palustris O.S. in
vhich mitosis was taking place the chromosomes were found to be eight
n number. They are slightly curved and show a decided tendency to
roup in pairs when moving out from the equatorial plate. The root
ips of the host Quercus coccinea Muench. were found to give the same
*hromatic count and the chromosomes present the same feature of moving
ut to the poles of the spindle in groups of two.

In several galls amitosis was noted and very marked examples in
he nutritive zones of the galls Aulacidea nabali Brodie (Text Fig. 6)
ind Aylax glechome Linné. Cell division did not appear to accompany
he phenomenon in any of the cases examined.

358 TRANSACTIONS OF THE CANADIAN INSTITUTE [VOL. I

In galls other than the Cynipidz, the only cytological phenomen
that presented unusual features were found in the orders Diptera an
Lepidoptera. An unusual type of cell division was observed in the corte
and epidermis of Neolasioptera perfoliata Felt (Text Fig. 7) and in th
cortex of Gnorimoschema galleasterella Kellicott and Stagmatopho
ceanothiella Cosens. This has been already referred to in the descriptiv
part of the paper and only the main features will be noted here. Th
mother cells produce from 2 to 5 daughter cells and these remain i
groups that are easily recognizable. The elongated nuclei are found i
contact with the septating walls but not exactly opposite each othe
In the Dipterous genus Neolasioptera this was the only form of ce
division that occurred in the gall, but in the Lepidopterous genera
was found only in a limited area of the abnormal tissue.

VU PLY 4
rc aeliass
Y, A a

Lae

Fig. 6.—Nuclei from the nutritive layer of Fig. 7.—Cell division in the epidermis and corte:
Aulacidea nabals Brodie. of Neolasioptera perfoliata Felt.

THE BEGINNING OF GALL DEVELOPMENT.

In some species of galls that originate from stems, veins or petiole
the eggs of the producer are deposited within the tissues of the host 1
or near the cambium zone. Adler and Kiistenmacher have detecte
eggs actually placed in that region, and while my own observations i
the case of Cynips? constricta Stebbins were made on older develo
mental stages, yet the nature and arrangement of the tissues were suc
as would seem to preclude any other conclusion. The origin of this ga
from the vein is shown in Fig. 53. In leaf galls that are produced in th
blade as Rhodites lenticularis Bass. (Fig. 63), a cambium is differentiate
in the mesophyll into which, in this case, the egg is inserted. Two inde
pendent observers, Beyerinck and Weidel, have demonstrated beyond
doubt, however, that the egg is in some cases placed on the epiderm:
of the host, and consequently there are at least two distinct methods
ovipositing.

912] MORPHOLOGY AND BIoLoGy oF INSECT GALLS 359

The two observers, who deal with the development of galls from
ggs deposited on the outside of the host, hold entirely different opinions
oncerning the early stages. Beyerinck!® supposes that after the egg is
laced at the selected spot, the tissues under it grow very little, if at all,

but those immediately adjacent undergo rapid proliferation until the
2gg is completely enclosed, forming a gall of the ‘‘'Umwallung” type.
According to his view the larva possesses the power to stimulate the
tissues through the egg membrane without rupturing it.

Weidel, on the other hand, holds an entirely different opinion con-
cerning the enclosing of the larva by the tissues of the host. He has been
able to convincingly demonstrate that in the gall Neuroterus vesicator
Schlecht, the cuticle of the leaf is punctured before the larva is completely
free from the egg membrane. ‘Die in der Eihaut noch vollstandig
singeschlossene Larve durchbricht diese an einer Stelle und senkt in die
Epidermis des Blattes ein Organ ein durch das die Cuticula durchbrochen
und das pflanzliche Gewebe verletzt wird.’—Weidel.* The influence of
the larva soon produces proliferation in the tissues of the leaf, and
following this a degeneration commences at the epidermis and extending
quickly forms a cavity of sufficient size to hold the larva. Into the larval
chamber thus prepared the producer gradually passes, and the opening
through which it entered is soon closed by the growth of the stimulated
tissues.

While the excellent work of Weidel cannot be questioned concerning
this particular gall, it is not necessary to assume that this is the only
method by which a larval cavity is formed. In my opinion the method as
described by Beyerinck is found in some of our American species of Andri-
sus and Dryophanta, reference to which will be made later. Weidel’s
»bjections contained in the following quotation do not seem serious
enough to warrant the setting aside entirely of the ‘‘Umwallung” type
of development. ‘“‘Gerade diese Stelle war es, die mich zu meinen Unter-
suchungen anregte, denn eine grosse Anzahl von Fragen bleibt bei diesen
Ausfiihrungen Beyerinck’s unaufgeklart: Wie kommt es, dass an der
Stelle, wo das von der Larve abgesonderte Enzym am starksten wirken
muss, keine Vergrésserung der Zellen stattfinden soll, sondern nur in
siniger Entfernung? Was wird aus Epidermis unmittelbar unter dem
Ei? Aus Beyerinck’s Figuren muss man annehmen, dass sie in Nahrge-
webe umgewandelt wird, da sie die Larve unmittelbar beriihrt. Wie
kommt das, ‘“‘Sinken,’’ oder, ‘‘ Vergraben,”’ zustande, Vorgange, fiir die
ihn seine Erklarungen selbst nicht befriedigen?’’—Weidel.*

Concerning the first question, as to why the proliferation is more
pronounced around the larva than in immediate contact with it, it may
be stated that this is a usual occurrence in the lower groups of galls in

360 TRANSACTIONS OF THE CANADIAN INSTITUTE [VOL. I.

which the stimulus is applied in one direction only. The stem mother
of the genus Chermes thus become surrounded by a ring of tissue tha
grows out around the point of attachment of the insect (Fig. 11). Th
Dipterous gall Cecidomyia ocellaris O.S. also furnishes a very strikin
example of this phenomenon. In this species the leaf is scarcely at a
thickened under the larva, but the proliferation is so marked around |
that the producer ultimately lies in a concavity, not formed by the lez
becoming depressed, but by the outgrowth of the circular ridge of tissu
(Fig. 33). Any explanations offered to account for these facts are merel
conjectural, but it seems likely that the enzyme content requires a certai
degree of concentration in order to exhibit its maximum activity, an
that immediately in contact with the larva it has not the requisite dilutio
to cause the greatest proliferation. It is a well-known fact that th
amount of growth of plants in culture solutions varies with the degree «
concentration of the nutrient substance in the medium; thus there is a
optimum quantity and as this is exceeded growth is more and mot
inhibited. An example of this is furnished by the checking of the growt
of Penicillium when the culture solutions are too concentrated.

With regard to the question, ‘‘What becomes of the epidermis und
the egg?’’ I agree with Weidel that there is little likelihood of abnorm:
cell production until the larva punctures the egg membrane, but whe
this occurs the epidermis becomes part of a nutritive zone and wi
undergo such rapid changes that its epidermal characteristics will soo
disappear. The chief alterations will be expressed in the much riche
contents of the cells and in their steady collapsing as these contents a1
withdrawn (Figs. 49, 51, 52). The latter change makes it extremel
difficult to follow the normal into the abnormal epidermis unless at a
extremely early stage. While the enclosing of the larva is due chiefly t
the growth of the surrounding tissues, yet the collapsing of the nutritiv
layer will assist it to a certain extent.

Weidel’s photographs show that in Neuroterus there is not at an
stage an opening into the larval cavity that is lined with the epidermis «
the leaf, and that after the larva enters its prepared chamber the openin
is very soon closed. In the method of development as stated by Bey
rinck we would expect to find such an opening persisting for some tim
and if we do, that must be accepted as confirmatory evidence of th
truth of his hypothesis. In two different genera, namely Dryophant
and Andricus, I have found canals leading into the gall cavity in tk
early developmental stages (Figs. 43-49). The epidermis of these stru
tures is continuous with the gall epidermis and it bears the same class «
trichomes as the latter. The canal is very marked in Dryophanta palu.
tris O.S., and its lining which is the same as the gall epidermis, can k

g12] MorPHOLOGY AND BIOLOGY OF INSECT GALLS 361

raced until it passes over into the inside layer of the nutritive zone
Fig. 49). This canal can still be detected in well-grown specimens.
Only mature material of Andricus piger Bassett and Andricus
eliolicola Bassett was obtained, and while the canals with the epidermal
ining are well marked, they are shut off from the larval cavity by out-
rowths of sclerenchyma from the protective sheath (Figs. 43, 44).
here is little doubt, however, but that in early developmental stages
hey open into the gall cavity as in the genus Dryophanta. This view, -
ndeed, I have practically confirmed in the examination of an undescribed
pecies of Andricus on Quercus macrocarpa Michx. In this form the canal
s blocked at maturity by sclerenchyma (Fig. 47) as in the former species,
ut at an early stage I have found it extending into the larval chamber.
Summary.
| The evidence seems conclusive that there are two types of early
developmental stages of galls when the egg is deposited on the epidermis
of the host. The method of formation of the larval chamber as described
by Beyerinck is found in certain genera, as Dryophanta and Andricus,
while the method worked out by Weidel occurs in Neuroterus and in all
probability other forms.

_FEEDING HABITS OF THE LARV2 OF GALL PRODUCERS.

With the exception of the family Tenthredinide, all gall-producing
larve have started to feed before the abnormal production of tissue
commences. The narrowing of the problem of gall production to the
influence of the larve on the tissues of the host has given additional
importance to the problems dealing with the feeding habits of these
larval producers.

Order Arachnida.

Fam. Eriophyide.

The members of this family have mouth parts of the sucking type.
With their cone-shaped beaks they pierce the cell walls and withdraw
the liquid contents. The cell walls are not used as food.

Order Hemiptera.

Fam. Aphidide.
Fam. Psyllide.

The feeding habits of these families are similar to the preceding.
The possession of a suctorial proboscis makes it possible for them to ob-
tain the liquid contents of the cells by merely puncturing the walls.

Order Lepidoptera.

The larve in this case consume the entire cells that line the interior
of the galls.

Order Coleoptera.

362 TRANSACTIONS OF THE CANADIAN INSTITUTE [VOL. 1

Feeding habits as in the preceding order.
Order Diptera.

Fam. Cecidomyide.

Fam. Trypetide.

Concerning the feeding habits of this order, Packard® states tha
the Cecidomyia larve must absorb their nourishment through the skir
or suck it in at the mouth. He bases his conclusion on the facts that the
larve are devoid of jaws and that excrement is not found in the mature
galls.

Walsh“ from the same data has come to the conclusion that the
larve abrade the interior of the galls with the chitinous structure, th«
so-called breast bone, on the ventral surfaces of their bodies. Thi
irritation produces a flow of liquid from the cells and upon this the larva
feed. He further states that the mouth of the larva of Eurosta solidagini.
Fitch possesses a horny, black termination that probably serves the
same purpose of abrasion as the breast bone of the Cecidomyide.

Both of these observers have concluded that the nourishment i:
obtained by the larve without the destruction of the cell walls, anc
that these do not form a part of the food of the larva. My observation:
confirm this view. In several species such as Lasioptera corms Felt anc
Cecidomyia ocellaris O.S. (Figs. 33, 40), the walls of the cells, througl
which the larve were obtaining food, were apparently uninjured. I1
other forms as Cecidomyia triticoides Walsh (Fig. 37), and Cecidomyic
pellex O.S., the cells of the nutritive zone had collapsed as the content:
were withdrawn.

Order Hymenoptera.

Fam. Tenthredinide.

By the time the larve in this family are full fed, nothing remains o
the galls but a thin rind on the outside of each. Both the cell walls anc
contents are swallowed indiscriminately.

Fam. Cynipide.

In this family the larvz are invariably surrounded by a layer o
thin-walled cells which usually present a radial elongation especially ir
the innermost rows (Fig. 58). The cells of this nutritive zone contai1
sugar, starch, oil emulsion and albumen. The amount of starch varie:
directly and the sugar inversely with the distance of the cells from th
larve.

With regard to the manner in which this zone is used as food by the
larva at least two views are current. The following statement of Kerner’
may be presented as an adequate expression of one of these theories
“The larva when hatched finds the inner wall of the chamber which ha:
been fitted for its temporary abode always provided with the necessary

ng12] MorPHOLOGY AND BIOLOGY OF INSECT GALLS 363

ood, and it immediately attacks and devours the juicy tissue with great
vidity. The cells which are demolished, wonderful to relate, are replaced

most at once. The cells of the gall pith remain capable of division as
ong as the larva in the chamber requires food, and the surface cells which
ave been devoured in the gall chamber are soon replaced by new cells.”

Kiistenmacher®* has advanced an entirely different view and his
pinion may be taken as representing the theory of the other school of
bservers.

He states,—‘‘ Die im Innern entschliipfte Larve, welche ihren Tisch
reichlich gedeckt findet, beisst die innern Zellen des Nahrungsgewebes,
welche lose, von der Eiweiss-Zucker-Oel-Emulsion strotzend, hervor-

agen, an und saugt dieselben regelmadssig ringsherum aus, wahrend die
ehr diinnen Wandungen schmal schlauchartig tibrig bleiben.”

In deciding between these two theories the question to be answered
is, does the larva eat both the walls and contents of the cells as stated by
Kerner, or does it extract in some way the contents of the cells, leaving
the walls practically intact? Several different points are involved in
the discussion of this question. (a) The absence of frass in the larval
chamber. (b) The completeness of the alimentary canal in the larva.
(c) The nature of the stomach contents. (d) The presence of collapsed
tissue and empty cells in the nutritive zone.

When a mature Cynipid gall is examined the larval chamber, in
which the producer has passed through its early stages, is found unsoiled
by excrement. Concerning this matter my observations agree with
those made by Walsh in respect to the Cecidomyia larve. By way of
comparison, if a mature gall is examined, the larva of which is known to
eat the entire cells, a comparatively large quantity of excreted material
is found (Fig. 68). The mature larva and its frass from a gall of Pontania
pomum Walsh were dried in a desiccator and weighed. The following
result was obtained:

Larva .O115 gm.

Frass .0319 gm.

In view of the comparatively large amount of frass in the sawfly gall, its
absence in those of the Cynipide appears significant.

This fact concerning the larve of the Cynipidz has not received
attention since it has been supposed that the intestine of the Cynipid
larva ends blindly. Comstock”! makes the tollowing statement on this
point: ‘‘The larve are maggot-like and without a caudal opening to
the alimentary canal.’ Serial sections were made of the larve of the
producers Philonix nigra Gill (Fig. 61), and Amphibolips confluens Harris
(Fig. 62). These sections prove conclusively the completeness of the

364 TRANSACTIONS OF THE CANADIAN INSTITUTE [VOL. 1x

intestinal tract throughout, and that therefore if Kerner’s theory be
correct frass should be found as in the sawfly galls.

Further evidence in favor of Kiistenmacher’s view is furnished by
a comparison of the stomach contents of a Cynipid and an inquilin
larva. The former consists of a mass of extremely fine particles, amon
which can be detected nothing that is recognizable as having formed
part of a cell (Fig. 55). As this material passes along the digestive tra
it becomes less dense the nearer it is to the posterior opening, and is en-
tirely absent in the last part of the canal (Figs. 61,62). The latter con-
sists of much coarser material in which crystals, similar to those in the
surrounding cells, and parts of cell walls can be easily detected. These
contents are shown in Fig. 56, and at a higher magnification in Fig. 57.
So characteristic is this difference between these two classes of stomach
contents that by means of it alone a Cynipid can be easily distinguished
from an inquiline larva.

The data already presented furnish indirect proof that only the
contents of the cells form the food of the Cynipid larva. An examination
of the walls of the cells immediately surrounding the larva gives direct
evidence in favour of this hypothesis. The nutritive layers of a large
number of Cynipid galls were examined at different stages of development,
and in none of the examples did the walls of the cells appear to have been
eaten away by the larva. A layer of collapsed tissue (Figs. 52, 59, 60),
especially in the older specimens, is often found around the inside of the
larval chamber and there are also many empty cells throughout the
nutritive zone. These are shown in the inner row of cells in Figs. 59, 60.
In some cases the radial walls of the cells are wrinkled, indicating tha
these cells are gradually contracting. This can be seen with the aid of a
lens in Fig. 59. The folds are not found in the tangential walls of the

n
cells. The majority of the empty cells are found in the row that lines
the interior of the larval chamber (Fig. 60), but others are distributed
irregularly throughout the entire nutritive zone. These can be seen in
Figs. 59,60. There does not seem to be the slightest possibility of doubt
that the larva withdraws the contents from the cells of the nutritive zone
without destroying the walls, and that in consequence the cells surrounding
the larva gradually collapse.

If an inquiline larva is feeding in the gall, a ragged, broken edge of
tissue is found lining the cavity in which it is living, a marked contrast
to the smooth interior of the Cynipid larval chamber. This uneven
edge is shown in Fig. 56, compare with Fig. 55. Neither of these views
takes into account the possibility of enzyme action in rendering more
soluble the contents of the nutritive zone.

1914] MorPHOLOGY AND BIOLOGY oF INSECT GALLS 365

A number of investigators have suggested that some form of enzyme
is secreted by the larve of the Cynipide. Kiistenmacher* indeed
states in this connection that he could detect a distinctive odor from
these larve, but enzyme action has always been considered in relation
to the gall-producing stimulus and never with the feeding habits. The
gradual decrease in the proportion of sugar to that of starch, in the con-
tents of the cells, from the inside of the nutritive zone to the outside,
would seem to indicate a relation between the relative amount of sugar
and the proximity of the larva. Experiments were accordingly under-
taken with the purpose of deciding whether the larva was capable of
producing this change and of thus rendering the cell contents more
easily soluble.

FIRST SERIES OF EXPERIMENTS.

Forty larve of Amphibolips confluens Harris just removed from the
galls were placed in about 7 c.c. of starch solution made of corn meal.
The test tube containing the larve was placed ina bath at 50° C., along
with a control.

This starch was tested for sugar with Fehling’s solution. No sugar
was found at the end of 2 hrs. but after 20 hrs. a test for sugar was readily
obtained.

SECOND SERIES OF EXPERIMENTS.

Forty-two larve were placed in the same quantity of starch solution
and treated as in preceding case.

No sugar was found at the end of 8 hrs. but after 12 hrs. from the
beginning of the experiment sugar was detected, and again at the end
of 24 hrs.

THIRD SERIES OF EXPERIMENTS.

Thirty-five larve were placed in 7 c.c. of water and left for about
3 hrs. This water was then placed in an equal quantity of starch solution
and kept at about 50° C. as before. The water was tested before it was
poured into the starch and found to give an acid reaction. In this case
sugar was detected in 50 hrs. and a very decided reaction was obtained
after 70 hrs. The larve that had been washed were placed in starch and
kept at 50° C. as before but sugar could not be detected.

In all the cases cited above, as a control experiment, starch without
the larve was kept in the bath under the same conditions as that which
contained the larve. This starch did not give the slightest indication
of sugar at any time. From these experiments we conclude that
the Cynipid larve must secrete an enzyme that has the property of
changing starch to sugar. It seems quite possible that other ferments
may be employed by the larva for similar purposes. To my knowledge

366 TRANSACTIONS OF THE CANADIAN INSTITUTE [VOL. Ix

no tests have been made, but the observations of Weidel* point con-
clusively in this direction. He noted that the walls of the protective
sheath become delignified; this is strongly suggestive of the presence of
a hadromase or allied ferment.

With the purpose of discovering the source of the enzyme a
number of species of Cynipid larve were examined for glandular
structures. An enlargement of the first two segments immediately
below the mouth was found to be a common characteristic of all these
specimens. Regularly arranged on these projections are two pairs of
openings as shown in Text Fig. 8. Longitudinal serial sections of
Philonix nigra Gillette and Amphibolips confluens Harris show that
these openings are connected by ducts with cavities lined by a glandular
epithelium composed of large cells. From these cells the enzyme
containing material passes into the cavity and from thence to the
outside by means of the duct. There seems little reason to doubt but
that these structures are salivary glands opening externally, and that
they are the source of the enzyme. A gland with the connecting duct
is shown in Text Fig.9. Only the two species mentioned have been
examined by serial longitudinal sections, but the external openings were
noted in several forms and in all probability these glands are a
characteristic common to all the Cynipide.

So @
8 ee ee
the salivary glands just below the mouth.

Concerning the feeding habits of the larve of the Cynipide, we can
state positively that the cell contents alone furnish the nourishment and
that these are withdrawn from the cells without destroying the walls.
An enzyme secreted by the salivary glands of the larva partially pre-
digests this food. This ferment must act through the *cell membrane

*I have found that the froth on plants in which the “Spittle Insects” of the
Family Cercopide develop, also contains an enzyme that rapidly changes starch to
sugar. Experiments by Miss J. McFarlane that are not yet fully completed seem to
indicate 2 larger amount of sugar in the stems surrounded by the froth than mm

corresponding parts of unaffected stems.

A

1932] MorrHotocy asp Biotocy of Insect Gals 37

lining the interior of the larval chamber. None of the nourishment,
taken into the alimentary canal, passes from it as excrement; it is
either completely absorbed or remains in the digestive tract until the

of food absorption through the body wall is quite untenable; since the
complete digestive tract, containing often large quantities of nourish-
ment, as in Fig. 62, shows conclusively that the food enters the canal
through the mouth.

GALL-Propucine STIMULUS

All actively growing tissues are capable of responding to a gall-
producing stimulus; the growth energy already present in them is eon-
trolled and compelled to expend itself in 2 definite direction. These
abnormal tissues that result have the common characteristic of remain-
ing longer in a plastic state than if they had been produced under normal
conditions of growth.

The stimulating influence produces an effect om tissues at 2 con-
siderable distance from the centre of application. Thus in the Acarina
galls this influence extends to tissues other than the epidermis on which
the mites are located, and in such 2 case 2s Stagmatophora ceanoth:dls
Cosens the epidermis of the stem undergoes division, although the larva
is feeding in the pith (Fig. 17).

The power to stimulate tissues to abnormal activity is not confined
to a limited extent. By a fortunate chance I have been able to establish
this fact in the case of an inquiline larva found in the gall of Holcaspis
. gobulus Fitch. Reference to Fig. 65 will show that 2 nutritive layer has
been developed around the inquiline. That it possesses the power of
stimulation to a less extent than the producer is obvious from the fact
that it was unable to originate 2 cambium of its own, and in consequence
- the nutritive zone is incomplete on the side opposite to the producer-
larva. This is shown in Fig 65. Yet it is equally obvious that, feading
as it was in proximity to the cambium of the producer, it was able to
excite that zone to the production of typical nutritive cells instead of the
parenchyma zone cells that would have resulted had the producer alone
been in control. Kiister® records 2 similar instance of inquiline-p-oduced
galls in Rhodsie: eglantcria.

Kiieter™ states that the excrement of the lerval Pontezia sakicis is
capable of producing cell division I have found this phenomencs
occurring also in Ponianis pomum Walsh and particularly good examples

368 TRANSACTIONS OF THE CANADIAN INSTITUTE [VOL. Ix

in the undescribed sawfly gall on Salix serissima (Bailey) Fernald (Fig.
72). While I have made no attempt to determine by experiment the
cause of this unusual example of cell proliferation, yet it would seem
highly probable that the enzymes, introduced into the protoplasm by the
ovipositor of the producer and swallowed by the larva, have not entirely
lost their power by passing through the digestive tract but are still able
to excite cell division.

The gall producer’s influence works remarkable changes in the
affected part of the host; even apparently new tissues, glands, trichomes,
etc., make their appearance. The activity of its protoplasm is so much
increased that hypertrophy or hyperplasia is an invariable accompani-
ment of gall production. The conventional view to account for these
phenomena is that the protoplasm has been endowed with entirely new
characteristics and power to produce something foreign to the normal
host. But this is probably true only in a very limited sense, for according
to my experience at least the prototypes of such apparently new tissues,
etc., have been found elsewhere in the host or its relatives. Seemingly
the correct explanation is that not only are dominant characteristics in
the protoplasm stimulated but also in certain cases latent properties are
called into activity, and thus apparently new structures appear in the
host. Attention has already been drawn to examples confirming this
opinion, but the evidence will now be more fully elaborated in the case
of glands, trichomes and aeriferous tissue.

It may be stated as an unvarying rule, that when glands are present
in the normal tissue they are always more plentiful or larger in the gall
originating from that tissue. This is exemplified in the galls produced
by Eurosta solidaginis Fitch (Fig. 42), Aulacidea nabali Brodie (Fig. 66),
and numerous other species to which attention has been directed in the
descriptive part of this paper.

But glands also occur in certain galls on parts of the host that are
normally glandless; thus they are plentiful in the gall produced by Neo-
lasioptera perfoliata Felt on Eupatoria perfoliatum L. (Fig. 23), but are
not found at the same location in the normal. At first sight they appeared
to be new structures, but were finally discovered in the normal host at
the base of the stem. In E. urticefolium Reichard they likewise occur
in the transitional region between stem and roor, while in LE. purpureum
L. they are present in the roots, petioles, and flowering axes as well as
in the cortex and pith of the stem. In the case of gland production it is
clear that not only have active characteristics of the protoplasm in that
direction been stimulated to an activity greater than the normal maximum
but nearly dormant properties have sometimes been aroused into action.

1912] MorPHOLOGY AND BIOLOGY oF INSECT GALLS 369

The trichomes worked out in a manner very similar to the glands.
When the gall produced typesdifferent from thenormal they were searched
for successfully on the reproductive axes of the host. The unicellular,
acicular hairs of Eriophyes querct Garman (Fig. 6) are totally unlike the
stellate hairs of the leaf, but their exact counterparts are found on the
reproductive axes of the host Quercus macrocarpa Michx. The much
convoluted type of hair present in the Acarina dimple gall on the leaves
of Acer negundo L. (Fig. 4) are found plentifully distributed over the
reproductive axes, although the normal leaf hairs are straight.

The production of aeriferous tissue in certain Salicaceous galls sub-
stantiates in quite as striking a manner the view I have advanced. These
galls contain examples of a typical aeriferous tissue, comparable indeed
to that found in such aquatics as Nymphza, Potamogeton or Saururus,
while in the corresponding part of the host it does not occur. Indeed,
this statement may be extended to include all the species of the host
genus. A cross section of the gall originated on S. cordata Muhl. by
Cecidomyia triticoides Walsh shows this tissue surrounding each larval
cell. It is present throughout the cortex of the stem and extends entirely
across the pith (Figs. 34, 35, 36). This tissue is found also in the gall
originated on the leaf of the same willow by Pontania pomum Walsh
(Fig. 77), but is not found in the normal tissues; indeed, the mesophyll
of the leaf of S. cordata Muhl. is peculiarly compact in structure. It is
figured by Cook” in the cortex of the stem gall produced on S. discolor
Muhl. by Cecidomyia rigide O.S.

With the purpose of determining the distribution of this tissue in
the normal stem a number of species of Salicacez were examined by
Mr. T. A. Sinclair and myself with the following results, a detailed
description of which will be published later. It was found in the primary
corcex of the stems of the following species and invariably more plentiful
at the nodes,—Salix humilis Marsh., S. alba L., S. rostrata Richards,
S. lucida Muhl., S. discolor Muhl., S. nigra Marsh., S. longtfokia Muhl.,
S. serissima (Bailey) Fernald, S. cordata Muhl., Populus delioides Marsh.,
P. balsamifera L., P. tremuloides Michx. and P. grandidentata Michx.
It was also differentiated to some extent in the pith of the stems of P.
balsamifera L. and P. deltoides Marsh., P. grandidentata Michx. and
P. tremuloides Michx. The only indication of this tissue found in the
stem pith of Salix was in sections through the bases of branches of
S. cordata Muhl. and S. alba L. Possibly it may be present in the corre-
sponding region in other species. It can be traced a greater distance from
the growing tip in the cortex of Populus than in Salix before it becomes
unrecognizable owing to compression. It is apparently nearly always
present in the pith and cortex of the reproductive axes of Populus and

370 TRANSACTIONS OF THE CANADIAN INSTITUTE [VOL. 1x

Salix. The leaf petioles of the following species were found to contain it,—
Populus balsamifera L., P. deltoides Marsh., Salix humilis Marsh., S. alba
L. and S. cordata Muhl. The tissue is developed much more plentifully
on the side adjacent to the stem.

In general then this tissue is indicated in the pith of the stem of
Populus but is restricted in Salix to the bases of the branches. It is well
represented in the primary cortex of the stems of both Populus and
Salix, rather better so in the case of the former genus. It is abundant
in such primitive regions as the reproductive axes, nodes and leaf traces.
Thus the unexpected appearance of this tissue in the galls cited is readily
explainable on the same grounds as in the case of glands and trichomes,
namely, the power to produce this tissue is latent in the protoplasm of
the host and it becomes sufficiently active to reinstate the tissue only
when the gall-producing stimulus gives rise to unusual conditions.

Concerning the nature of this powerful stimulating agent there is
at present a growing tendency to ascribe it to enzymatic action. It is
difficult to say just how wide the application of this method of stimulus
may be, but as plants present so many features in common in their re-
actions to produce the different types of galls, universal enzyme action
would seem to be at least a safe working hypothesis. It is only, however,
in the case of the Cynipide that we have any experimental evidence
concerning enzymatic action. As described in a previous part of this
section, I have been able to prove, in the case of the gall Amphibolips
confluens Harris, that the larva secretes an enzyme capable of changing
starch to sugar. It is now my purpose to discuss this fact in its relation
to gall production.

Kiister,*4 after experimenting with Cynipid galls in culture solutions,
arrived at a conclusion that furnishes some experimental data on the sub-
ject. ‘‘Bei normaler Entwickelung wird der Inhalt der Nahrgewebe von
den Gallentieren verzehrt; unter abnormalen Verhaltnissen kann aber
das Nahrmaterial von den Pflanzenzellen selbst verbraucht werden.
Gallen von Pediaspis Aceris (Cynipide), die von ihren Bwohnern be-
freit und auf nahrstoffarmen Lésungen oder auf gewdhnlichem Leitungs-
wasser belassen werden, bleiben wochenlang am Leben; der Inhalt der
Nahrgewebe schwindet dabei. Werden Gallen gelicher Art ceteris paribus
auf Zuckerlésung verbracht, so bleibt der Inhalt der Nahrgewebe un-
verbraucht oder erfahrt noch eine geringe Vermehrung.”’

These experiments prove that a gall is able to extract nourishment
from the nutritive zone to assist in its growth in general. It appears
axiomatic then that the greater the quantity of soluble food there is in
the nutritive layer, in excess of what the larva requires, the larger is the
supply the gall has at its command and the more marked will be the

1912] MorRPHOLOGY AND BIOLOGY OF INSECT GALLS 371

proliferation of gall tissue. The larva consequently by accelerating the
rate of change from starch to sugar is indirectly stimulating the proto-
plasm and thus controlling the growth of the gall. The general principle
is applicable here that the available food supply governs very largely the
size of an organ and consequently must influence the activity of its pro-
toplasm. It is interesting to note in this connection that the size of the
gall and the contained larva are directly proportional to each other.
The relations between the two are reciprocal. The larger larva ensures
a greater enzyme production and hence a more abundant food supply
and presumably a larger excess for the stimulation to cell proliferation.
The amount of enzyme action appears clearly to be proportional to the
size of the larva. The evidence seems conclusive that the nutritive zone
functions as an organ for preparing soluble food materials for both the
larva and the gall. This evidence receives further confirmation from the
fact that in addition to the empty cells lining the larval chamber there
are others scattered throughout the nutritive zone often to its outermost
layers (Fig. 59). This also seems to point to the conclusion that the con-
tents of these cells have been used in supplying food for the proliferation
of tissue in the other parts of the gall.

Summing briefly, the larva secretes an enzyme, capable of changing
starch to sugar, which acts on the starchy constituents of the nutritive
zone and accelerates the rate of their change to sugar. The material
thus prepared supplies nourishment for both the larva and the gall. The
protoplasm of the latter is thus rendered unusually active since it re-
ceives an abnormal quantity of available food material in a limited area.
The hypertrophy and cell proliferation and probably also the appear-
ance of vestigial tissue or other primary characters are the response of the
protoplasm of the host to the additional food supply.

Attempts were made to substantiate this theory by further and more
direct experiment. Diastase in solution was injected into seedling
Windsor beans at different points with the purpose of stimulating the
tissues to increased cell proliferation. When the place selected was just
below the arch of the hypocotyl, a decidedly large callus was obtained in
some of the experiments. These were not conclusive, however, owing to
the variation in size of the normal plant in that region and the very great
if not insurmountable difficulty of detecting increased callus formation
when only differences in amount are to be expected. It is further very
difficult to simulate the action of the producer-larva in bringing the
diastase into contact with the proper tissue.

The discovery of an enzyme as an exudation from gall-producer larvee
recalls the statement of Laboulbéne* that he had induced cell proliferation
by injecting into plant tissue the water in which larve had been washed.

372 TRANSACTIONS OF THE CANADIAN INSTITUTE [VOL. Ix

The theory, just stated, furnishes an explanation intended to account
only for the stimulation of the protoplasm expressed in cell proliferation,
hypertrophy and the production of unusual structures. There are other
gall characteristics, however, that can scarcely owe their origin to the
action of enzymes alone on the protoplasm of the host. For example,
the colour of galls appears to be controlled partly at least by the intensity
of the illumination. Thus the galls produced on Salix cordata Muhl. by
Pontania pomum Walsh are little, if at all, coloured when the host is grow-
ing in deeply shaded stations. Besides this environmental effect, how-
ever, there is another factor that may also have an influence on the
colour of this gall. De Vries* states that the red colour in plants is a dor-
mant characteristic in the protoplasm that can be reinstated by stimu-
lation. As a distinct confirmation of his view he found that red tints
were produced in the leaves of Viburnum opulus L. as a consequence of
bruising. This experimenc seems to be closely paralleled in the sawfly gall
Pontania pomum Walsh, where a red colour is apparent in the leaf of Salix
cordata Muhl. in a very short time after oviposition. It seems very
probable that in this case as in that of Viburnum the dormant red char-
acteristic has been reinstated by the mere mechanical injury. It is note-
worthy in this connection that shades of red are the predominating tints
in gall structures, so that in the production of colour enzymatic action
may frequently be operative in reinstating che dormant character red,
especially in the case of galls in which che mechanical injury is negligible.

Further, the shape of the gall and the relation of the various zones
to each other are not explainable by reference to any one factor. They
doubtless result from a combination of factors. Just what all of these
may be is yet not apparent but this much is certain that there appears to
be an entire lack of evidence supporting the view that the protoplasm
of the host has become endowed with a property that enables it to pro-
duce a fairly definitely shaped but withal abnormal structure. Such a pro-
nounced change would surely be expressed in the hereditary character-
istics, yet there is not a vestige of proof tending to show that insect galls
ever produce the slightest variation in the descendants of the host. Not
only so, but in the case of stems growing beyond the gall, there is no
certainty that the prolongations are abnormal except for the slight
dwarfing which is possibly explainable on the basis of an interrupted food
supply. Examples of such stems are furnished by Cecidomyia triticoides
Walsh on Salix, Chermes abietis Linn. on Picea, or Eurosta solidaginis
Fitch on Solidago. Kiister also found in his regeneration experiments
that the roots produced from specimens of Pontanta salicis were perfectly
normal. There is still another argument to be cited in opposition to this
view, in the fact that one gall may be parasitic on another. Thus when

gia) MORPHOLOGY AND BIOLOGY OF INSECT GALLS 373
jorhiza forticornis Walsh is produced on Neuroterus batatus Fitch the
timuli from the different producers are exerted on nearly the same
ion of the host at the same time, as both these species are stem galls
commence to develop just as the buds are opening. In such a case
this if we assume that the protoplasm of the host has acquired char-
cteristics necessary to the production of a certain form of gall, it seems
kely that it could also possess the characteristics that would enable
t to originate an entirely different type at the same time.

With the exclusion of the likelihood that the genetic characteristics
“the protoplasm have been modified in any way, we must turn to the
‘nvironmental factors to account for the shape of the gall and the re-
ations of its various zones. Among these one feature that must have a

in amount of controlling effect is the direction in which the stimulus
Be sied, The various types of dimple and pouch galls, in which a curv-
ing of the affected organ is a very marked feature, are originated by
timuli disseminated in one direction only, while a Cynipid gall with its
i. spherical inner gall arises when the influence is about
equally distributed in all directions. In some species it is also clear that
the location of the egg has produced an effect on the external form of the
gall. If the egg is deposited on the epidermis of the host and the tissues
row up around it, a gall of the type produced by Cecidomyia ocellaris O.S.
results (Fig. 33). Even in the Cynipide this factor has been in operation.
In species of Andricus the openings of the canals give a characteristic
appearance to the galls, and in A. petiolicola Bassett the gall is drawn out
to a decided tip in the region of the canal. These canals owe their origin
to the fact that the galls are of the ‘‘Umwallung”’ type, and the larve
have been enclosed by the growth of the surrounding tissues.

In some galls such as Dryophania palustris O.S. a cambium is differ-
entiated at a very early developmental stage, and has a very marked in-
fluence on the general relation of the zones in the gall. This cambium
layer is shown in Fig. 49. The cells produced from the inside of this
cambial tissue constitute the nutritive and sclerenchyma zones, while
those given off from the outside form the parenchyma zone and epidermis.
The former that are under the immediate control of the larva and less
exposed to external conditions come to differ more markedly from the
normal than do the latter that are nearer the outside limit of the larva’s
sphere of influence.

374 TRANSACTIONS OF THE CANADIAN INSTITUTE [vou.

Summary.

The idea that the gall-producing stimulus must of necessity
applied directly to the cambium layer is not true im all cases, as
actively growing tissue will respond to 2 producer’s influence.

The effect of this stimulus is operative on tissue at a
distance from the centre of application.

Certain inquilines im Cynipid galls possess the gall-producing
but to a less extent than the real producer.

Cynipid producers and probably others secrete an amylalytic
that pre-digests food for the larva and may indirectly stimulate
proliferation by storing the nutritive zone with an unusually large
tity of available nourishment which can diffuse to all parts of the gall.

The gall-producing stimulus renders the protoplasm of the
more active and awakens m it dormant characteristics, but
does not endow it with power to produce entirely new structures.
has been demonstrated im the case of glands, trichomes and
tissue.

The red colour of galls is perhapsadormant characteristic that
be reinstated by enzymatic action but there are other possible f
factors such as the light relations and in sawfly galls mechanical
by the act of oviposition.

leaving the egg, this feature has no effect.
The relation of the various zones in the Cynipid galls is
im some cases by the early differentiation of 2 cambrum layer.

| pia] MORPHOLOGY AND BIOLOGY oF INSECT GALLS 375

LITERATURE CITED.

. Adler, H., Uber den Generationswechsel der Eichengallwespen. Zeit.
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. Anderson, A. P., Comparative anatomy of the normal and diseased
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. Beutenmiiller, Wm., Monograph of the Sesiide. Amer. Mus. Nat.
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. Beutenmiiller, Wm., The North American species of Rhodites and
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. Beutenmiiller, Wm., The species of Holcaspis and their Galls. Amer.
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. Beutenmiiller, Wm., The species of Amphibolips and their Galls.
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. Beutenmiiller, Wm., The species of Biorhiza, Philonix and allied
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. Beutenmiiller, Wm., Some North American Cynipide and _ their
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- Beutenmiiller, Wm., The North American species of Aulacidea and
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. Beutenmiiller, Wm., The North American species of Dryophanta and
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15. Beyerinck, M. W., Beobachtungen itiber die ersten Entwicklungs-
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16. Brodie, Wm., Cecidomyia bulla Walsh. Biol. Rev. Ont., vol. 1, No. 3, |
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17. Brodie, Wm., Lepidopterous Galls from Toronto. Can. Ent., vol. 41,
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378

Fig.

Fig.

Fig.

Fig.

Fig.

Fig.

Fig.

Fig.

Fig.

Fig.

Fig.

Fig.

10.

Il.

12.

TRANSACTIONS OF THE CANADIAN INSTITUTE. [VOL. 7

EXPLANATION OF PLATES.
PLATE I.

Eriophyes Sp. (Populus tremuloides Michx.). Section showing
the folding of the upper epidermis of the leaf. X 50.
Eriophyes Sp. (Populus grandidentata Michx.). Section showin

the nature of the folding produced on the lower surface of the
leaf. X60,
Eriophyes Sp. (Fagus grandifohia Ehrh.). Section through a
number of capitate trichomes. The almost normal character of

the leaf is shown. X 50.
Eriophyes Sp. (Acer negundo L.). Section through the gall,
showing a large number of convoluted trichomes. X35:

Eriophyes Sp. (Prunus nigra Ait.). Longitudinal section in
which is shown the elongation of the cells in the direction of the
long axis of the gall. The peculiar nature of the trichomes is
also shown. X30.
Eriophyes querct Garman (Quercus macrocarpa Michx.). Section
in which the long acicular trichomes are shown, as also the thick-
ening of the leaf blade. X 30.
Unclassified gall on the leaf of Populus balsamifera L. The
uniform nature of the abnormal cells is apparent. The gall

cavity is occupied by the mycelium of a fungus. X10.

Transverse section of band of sclerenchyma from the preceding

gall, showing the pores that traverse the tissue. X 120.
PLATE;

Aphid corrugations on the leaf of Betula lenta L. produced by
the fourth generation of Hamamelistes spinosus Shimer. The
formation of the larval chambers by the closing of the folds is
shown. X22.
Hamamelistes spinosus Shimer on the leaf of Hamamelis vir-
gintana L. ‘Transverse section that passes through a spine,
cross sections of two bundles are shown. M35.
Chermes abietis Chol. on the stem of Picea abies (L) Karst.
Longitudinal section, showing two larval chambers with their
apertures of exit. A number of resin ducts are cut near the
margin of the section. X30.
Hormaphis hamamelidis Fitch on the leaf of Hamamelis vir-
giniana L. Longitudinal section passing through the aperture
of exit. X10.

191]

Fig.

Fig.

Fig.

Fig.

Fig.

Fig.

Fig.

Fig.

Fig.

Fig.

Fig.

Fig.

13

14.

16.

17.

18.

19.

20.

2I.

22.

23.

24.

MORPHOLOGY AND BIOLOGY OF INSECT GALLS 379

. Chermes floccus Patch on the stem of Picea mariana (Mill.)
B.S.P. Transverse section, showing the smaller accessory resin
ducts. X25.
Pemphigus rhois Walsh on the leaf of Rhus typhina L. Longi-
tudinal section of a young gall, showing a number of glands. X15.

PLATE III.

. Pachypsylla celtidis-mamma Riley on the leaf of Celtis occiden-
talis L. Section through the larval cavity, showing the cambium
tissue and the sclerenchyma sheath bordering it on the outside.

X15.
Memythrus tricinctus Harris on the stem of Populus tremuloides
Michx. Cross section through the thickened annual rings, show-
ing the clumps of bast fibres. X20.

Stagmatophora ceanothiella Cosens on the stem of Ceanothus
americanus L. Cross section, showing secondary growth in the
wood and the abnormal glands in the cortex. X50.
Normal stem of the host of the preceding species. Section
taken near the gall; glands are not present in the cortex. X50.
Glands found in the cortex of S. ceanothiella Cosens; these corre-
spond to those shown in Fig. 17. 150.

Gnorimoschema gallesolidaginis Riley on the stem of Solidago
canadensis L. Transverse section showing an abnormally large
gland in the cortex. X45.
PLATE IV.
Eucosma scudderiana Clemens on the stem of Solidago canadensis
L. Transverse section showing the proliferation in the bundles
and the medullary rays and also the enlarged glands in the
cortex. X75-
Gnorimoschema gall@asterella Kellicott on the stem of Soli-
dago latifolia L. A transverse section through one side of the
aperture of exit, the material used by the larva in smoothing
the sides of the hole for the reception of the plug is shown.
The cross checking in this material can also be seen. X 120.
Neolasioptera perfoliata Felt on the stem of Eupatorium per-
foliatum L. Transverse section showing an unusual type of
cell division in the cortex and epidermis of this gall. The glands
shown near the inner boundary of the cortex are not found in
the normal stem at the same height. X55-
Rhabdophaga strobiloides Walsh on the stem of Salix cordata
Muhl. Longitudinal section showing the larva in contact with
the small celled tissue at the apex of the stem. Xas5.

380

Fig.

Fig.

Fig.

Fig.

Fig.

Fig.

Fig.

Fig.

Fig.

Fig.

25.

26.

27.

28.

29.

30.

he

32.

33;

34.

TRANSACTIONS OF THE CANADIAN INSTITUTE. [VOL. I

Rhabdophaga batatas Walsh on the stem of Salix humilis Mars
A transverse section that shows the larval chamber surrounde
by a nutritive zone which is bounded on the outside by a we
defined protective sheath. X2
A part of the protective sheath of the preceding species e
larged to show the unequal thickening of the tangential wall
X200
Cecidomyia majalis O.S. on the leaf of Quercus coccinea Muenc
Section at right angles to the midrib. The folding of the lea
is shown and the uniform character of the mesophyll of th
gall. The epidermis lining the gall cavity is shown intact. XI

PLATE V.

Abies balsamea (L.) Mill. Transverse section of normal leaf
X35

Cecidomyia balsamicola Lintner on the leaf of A. balsamea (L.

Mill. Transverse section showing the folding of the leaf an
the elongation of the mesophyll cells. The irregularity o
the cells in the strengthening layer of the resin ducts can also
be seen. X35.
C. balsamicola Lintner on the leaf of A. balsamea (L.) Mill.
Transverse section through the midrib. The chief points
shown are the irregularity in the development of the endo-
dermis, the large amount of the transfusion tissue and the
relatively small amount of the non-pitted parenchyma. X100.
Abies balsamea (L.) Mill. A section, through the midrib of a
normal leaf, corresponding to the preceding section (Fig. 30).
X 100.
Cecidomyia impatientis O.S. on Impatiens biflora Walt. Sec-
tion through a larval chamber, showing the general nature of
the cells of the gall and the smaller cells of the nutritive layer.
The two dark masses attached to the nutritive tissue in the
lower part of the gall cavity consist of the mycelium of a fungus.
X30.

Cecidomyia ocellaris O.S. on the leaf of Acer rubrum L., showing
the almost unchanged character of the leaf immediately below
the larva and the great amount of proliferation in the region
surrounding it. The general arrangement of the cells at right
angles to the leaf blade is also shown. X30.
Cecidomyia triticoides Walsh on the stem of Salix cordata Muhl.
Transverse section in which is shown the general arrangement
of the larval chambers and the distribution of aeriferous tissue
throughout the cortex and pith of the gall. X10.

1912]

Fig. 35.

Fig. 36.

Fig. 37.

Fig. 38.

Fig. 39.

| Fig. 40.

Fig. 41.

MorPHOLOGY AND BIOLOGY oF INSECT GALLS 381

PLATE VI.

Cecidomyia triticoides Walsh on the stem of Salix cordata Muhl.
Transverse section showing the character of the aeriferous
tissue. X50.
Cecidomyia triticoides Walsh on the stem of S. cordata Muhl.
Transverse section of a young gall, showing the well defined
nutritive layer lining the larval cavity and the protective zone
bounding this tissue on the outside. The aeriferous tissue is
also shown. X 60.
Cecidomyia triticoides Walsh on the stem of S. cordata Muhl.
Transverse section through the nutritive and protective zones
of a mature gall. At the top of the figure is a dark band of
collapsed nutritive cells; below that a lighter coloured and
wider band of sclerenchymatous cells, the lumen of each filled
with a crystal of calcium oxalate; and below that again a layer
of cambium of nearly the same width as the preceding zone.

X 150.
Cecidomyia triticoides Walsh on the stem of S. cordata Muhl.
Transverse section of a young gall, corresponding to the pre-
ceding mature form. The nutritive zone is at the top of the
figure, its cells are filled with rich protoplasmic contents, with
the exception of those in the upper row and a fewscattered ones
throughout the zone. The protective zone is shown below this
tissue, but the cambium layer is not differentiated in the early
stages. X 150.
Cecidomyia bulla Walsh on the stem of Helianthus divaricatus L.
Transverse section through stem of host and attached gall,
showing the elongation of the fibro-vascular bundles in the
direction of the gall axis and the very marked proliferation in
the medullary rays. At the upper part of the figure, in the
gall cortex, an enlarged gland is partly shown and also other
glands at the junction of the gall and the stem of the host. X18.
Lasioptera corni Felt. on the leaf of Cornus alternifoia L. The
section shows the lower epidermis and one row of mesophyll
cells in normal position and also the strongly curved character
of the upper epidermis and the remaining mesophyll cells.
The normal appearance of all the cells is also apparent. x18.
Lasioptera impatientifolia Felt. on the leaf of Impatiens biflora
Walt. Section at right angles to the midrib, showing the
generally uniform character of the cells. Cells containing the
mycelium of a fungus are shown a short distance in from the

382

Fig.

Fig.

Fig.

Fig.

Fig.

Fig.

Fig.

Fig.

42.

43.

45.

46.

47.

48.

49.

TRANSACTIONS OF THE CANADIAN INSTITUTE. [VOL. Ix

gall cavity and above it. These cells give a false appearance
of a protective zone. X20.
Eurosta solidaginis Fitch on the stem of Solidago canadensis L.
Transverse section, showing the proliferation of glandular tis-
sue and the general arrangement of the glands along the lines
of the fibro-vascular bundles. X25.

PLATE VII.

Andricus piger Bassett on the leaf of Quercus coccinea Muench.
At the lower part of the figure a thick nutritive layer is shown,
bordering the larval chamber; outside of this tissue is the pro-
tective zone from which a cone-shaped projection originates
that blocks the canal leading in from the outside. The epider-
mis lining this canal is shown continuous with the general epider-
mis of the gall. X25.

. Andricus piger Bassett on the leaf of Q. coccinea Muench. Sec-

tion showing a nearly complete larval chamber. The other
parts correspond to those in the preceding figure. The epider-
mis lining the canal is not shown so well in this case, as the section
passes along the edge of the canal. X25.
Andricus petiolicola Bassett on the leaf of Q. alba L. Section
passing through the main canal. The epidermis of the gall is
shown passing into the trichome bearing lining of the gall. X25.
Andricus petiolicola Bassett on the leaf of Q. alba L. Section
passing through the termination of the main canal, showing a
number of trichomes and two larval chambers blocked by masses
of sclerenchyma. X45.
Andricus (undescribed) on the leaf of Quercus macrocarpa
Michx. Section passing through the edge of a canal and show-
ing the two masses of sclerenchyma almost united. X35.
Andricus imbricarie Ashmead on the stem of Q. coccinea
Muench. Section showing the numerous bands of cells radi-
ating out from the boundary of the protective sheath, the light
coloured layer in the figure. The darker coloured nutritive zone
bounds the protective layer and lines the gall cavity. X20.

PLaTE VIII.

Dryophanta palustris O.S. on the leaf of Quercus coccinea Muench.
Section of a very early stage in which the inner and outer
galls are still in contact. The following points are shown, a
canal passing from the outside into the larval chamber, the

1912]

Fig. 50.

Fig. 51.

Fig. 52.

Fig. 53.

Fig. 54.

Fig. 55.

Fig. 56.

MORPHOLOGY AND BIOLOGY OF INSECT GALLS 383

trichome bearing epidermis of the gall continuous with the
lining of this canal and passing into the inner row of cells of
the nutritive zone, the bay-like depression in this zone where
the canal enters. X30.
Dryophanta palustris O.S. on the leaf of Q. coccinea Muench.
Section of a somewhat more mature stage than the preceding,
showing the commencement of the separation of the inner gall
from the outer in the region of the cambium layer. X12.
Dryophanta palustris O.S. on the leaf of Q. coccinea Muench.
Section of the wall of the inner gall, showing the nutritive zone
with a line of collapsed cells next the larval chamber and a row
of empty cells just inside the collapsed tissue. The protective
layer borders the nutritive on the outside and a few round cells
of the parenchyma adhere to the protective zone. X70.
Dryophania palustris O.S. on the leaf of Q. coccinea Muench.
Section of the larval chamber of a mature specimen, showing
the insect breaking out of the inner gall. At this stage the
nutritive layer has entirely collapsed. X15.
Cyntps ? constricta Stebbins on the leaf of Q. coccinea Muench.
Longitudinal section showing the origin of the gall from the
midrib of the host in the region of the cambium layer. XIOO.
Cynips ? constricta Stebbins on the leaf of Quercus coccinea
Muench. Longitudinal section of an early developmental
stage showing the general structure of the gall. The dark mass
at the top of the figure represents the supplemental nutritive
zone of the gall; it is separated from the spherical part of the
gall by acambium tissue. The protective sheath that separates
the nutritive from the cambium in later stages is not yet dif-
ferentiated. A nutritive zone is also shown lining the larval
chamber. . X 40.

PLATE IX.

Holcaspis bassetti Gillette on the stem of Quercus macrocarpa
Michx. Section through the gall cavity with enclosed larva.
The character of the cells of the nutritive zone is shown and the
unbroken edge of its inside boundary. The finely divided
material of the stomach contents of the larva is also shown. X60.
Section of a larval inquiline from the gall Holcaspis bassetti
Gillette. The broken edge of the tissue on which the larva
has been feeding is shown, also the comparatively coarse material
of the stomach contents. X60.

384

Fig.

Fig.

Fig.

Fig.

Fig.
Fig.

Fig.

Fig.

Fig.

57:

58.

59.

60.

61.
62.

63.

64.

65.

TRANSACTIONS OF THE CANADIAN INSTITUTE. [VOL. Ix

Contents of the stomach of the preceding inquiline. The black
masses are parts of cell walls, while the lighter roundish particles
are crystals. X 300.
Holcaspis bassetti Gillette on the stem of Q. macrocarpa Michx.
Section through the nutritive zone of a nearly full grown speci-
men. The nutritive zone is shown to consist of elongated cells
next the larval chamber and elliptical further out. The dark
zone is a crystal layer that bounds the nutritive zone on the
outside. A cambium is differentiated between the nutritive
and the parenchyma layers but it is not well shown in the figure.

X60.
Andricus singularis Bassett on the leaf of Quercus rubra L.
Section through the nutritive and protective zones, showing
empty cells throughout the nutritive layer and the wrinkling
of the radial walls of its cells in general. X 100.
Aylax glechome Linné on the leaf of Nepeta hederacea (L.)
Trevisan. Section through the nutritive and protective zones,
showing the unbroken lining of the gall cavity and the row of
empty cells that borders the larval chambers. X8o.

PLATE X.

Philonix nigra Gillette. Longitudinal section of the larva,
showing the external opening of the alimentary canal. XI5.
Amphibolips confluens Harris. Longitudinal section of the
larva, showing the completeness of the digestive tract. XI5.
Rhodites lenticularis Bassett on the leaf of Rosa blanda Ait.
Section through the larval chamber, showing the nutritive
layer lining it. Bordering this tissue on the outside is the cam-
bium zone from which practically the entire gall is originated.
The dark band shown plainly at the right.of the figure is the
protective sheath. X20.
Philonix erinacei Beut. on the leaf of Q. alba L. Section in
which the four typical zones of a cynipid gall are shown, namely
nutritive, protective, parenchyma or tannin, and epidermal.
The sclerification can be seen to have passed out into the par-
enchyma zone. X25.
Holcaspis globulus Fitch on the stem of Q. alba L. Section
through adjoining larval chambers of a producer and an in-
quiline. a complete section of the latter is shown. The nu-
tritive tissue that supplies the inquiline with nourishment can

1g12]

Fig. 66.

Fig, 67.

Fig. 68.
Fig. 69.
Fig. 70.

Fig. 71.

Fig. 72.

Fig. 73.

Fig. 74.

MORPHOLOGY AND BIOLOGY oF INSECT GALLS 385

be seen to have originated entirely from the cambium differ-
entiated by the producer of the gall. Its irregularity on the
side opposite to the producer is very marked. X30.
Aulacidea nabali Brodie on the stem of Prenanthes alba L.
Section through the stem of the host and the attached gall.
The relation of the cambium of the host to the cells of the gall
tissue is shown. X30.

PLATE XI.

Neuroterus majalis Bassett on the leaf of Quercus alba L. Sec-
tion through a larval chamber containing the pupa of the pro-
ducer. The dark band around the inside of the gall cavity con-
sists of the collapsed nutritive zone and the protective layer.
At the upper right of the figure the general nature of the cells
of the parenchyma zone is shown. X50.
Euura S. gemma Walsh on Salix humilis Marsh. Section through
a mature gall, showing a larval chamber containing a pupal
producer and several large masses of excrement. The general
nature of the small celled tissue of the gall is also shown. X30.
Euura (N.S.) on the leaf of Salix serissima Fernald. Trans-
verse section, showing one uninjured bundle of the petiole and
the parts of two others widely separated by the proliferation
of the tissue stimulated by the laceration of the bundles. X35.
Euura (N.S.) on the leaf of Salix serissima Fernald. Section
of a younger stage than the preceding, showing as before one
uninjured and two injured bundles. X35.
Euura ovum Walsh on the stem of Salix humilis Marsh. Trans-
verse section through the stem of the host and the gall originated
from it. It shows the wedge-shaped cavity occupied by the
gall mass and the origin of the latter from a cambium tissue at
the boundary of the pith of the host. X18.
Euura (N.S.) on the leaf of Salix serissima Fernald. Section
of the gall showing proliferation induced by the excrement of a
larval producer. x18.

PLATE XII.

Pontania hyalina Norton on the leaf of Salix alba L. Section
of gall with larva still within the egg membrane. Prolifera-
tion is shown well advanced in all the tissues of the leaf. X35.
Pontania hyalina Norton on Salix alba L. Section showing
the wound of the ovipositor. X25.

486

Fig.

Fig.

Fig.

Fig.

Fig.

Fig.

Fig.

Fig.

Fig.

75:

76.

77:

78.

79.

80.

81.

82.

83.

TRANSACTIONS OF THE CANADIAN INSTITUTE. [VOL. Ix

Pontania hyalina Norton on the leaf of Salix alba L. Section
of a more mature stage than numbers 73 and 74. The amount
of gall tissue derived from the various sources can no longer
be distinguished. The uniformity of the tissue is very marked.

X25.
Pontania pomum Walsh of the leaf of Salix cordata Muhl. Sec-
tion through an early developmental stage in which the larva
had not freed itself from the egg membrane. There is shown
the laceration of the bundle of the midrib by the ovipositor and
the proliferation in the various tissues of the leaf. X20.

Pontania pomum Walsh on Salix cordata Muhl. Section of a
nearly full-grown gall, showing the distribution of the aeri-
ferous tissue and the location of the vascular strands. x18.

Pontania (N.S.) on the leaf of Salix humilis Marsh. Section
at right angles to the midrib of the leaf to which the gall is
attached. The general character of the gall tissue is shown and
the distribution of the vascular strands from the wounded
bundle. X20.

Pontania (N.S.) on the leaf of Salix humilis Marsh. Section

through the midrib from which two galls had originated. The

bundle is shown completely severed. x8.
PLATE XIII.

Pontania desmodioides Walsh on the leaf of Salix humilis Marsh.
Section through a chamber containing an unhatched larva.
Proliferation is well marked in all the tissues of the leaf. X40.

Pontania pisum Walsh on the leaf of Salix discolor Muhl.
Section of a mature gall, showing the general character of the
tissues. The dark band at the upper right of the figure marks
the line of attachment of the gall to the blade of the leaf. Just
beneath this line the proliferation in the palisade parenchyma
is shown. . X20.

Undescribed gall on the leaf of Salix lucida Muhl. Section of
a young gall on the midrib, showing the commencement of the
proliferation in the pith of the bundle. X20.

Normal Jeaf of S. lucida Muhl. Section through midrib for
comparison with the preceding. X25.

1912]

Fig. 84.

Fig. 85.

MORPHOLOGY AND BIOLOGY OF INSECT GALLS 387

Undescribed gall on the leaf of Salix lucida Muhl. Section
of a well-grown gall on the leaf petiole. The two arms of the
bundle are shown widely separated by proliferation set up
in the pith. The arrangement of the cells of the gall tissue
in curved rows is shown and the presence of elongated air
spaces between these. X15.
Undescribed gall on the leaf petiole of Salix humilis Marsh.
Section showing the ovipositor wound. Around the edge
of the incision is shown the cambium tissue from which the
greater part of the gall tissue has been produced. x18.

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