S batatus n. sp.
On S humilis (S cordata? and S discolor?)
A polythalamous gall of very variable shape and size, pale green when young, the color of the bark when mature, growing on twigs .06 — .19 inch in diameter, almost 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 occasionally give birth to a shoot, and it then reaches 1.35 inch in length and .60 inch in diameter. Sometimes it resembles a young apple pierced lengthways by a twig, and it then attains a diameter of .50 inch. Sometimes it forms a hemispherical or hemielliptic swelling, like a bunnion, on the side of the twig and attains a diameter of .30 inch. Sometimes all these different shapes are strung together one after the other in more or less close proximity, on the same twig. Sometimes it is reduced to a small, elongate-oval enlargement of the twig for 1/2 or 3/4 an inch ; and occasionally it becomes so irregular and so full of side-shoots, bulges, cracks, roughnesses and lobes, as to defy description. Very rarely it is terminal and assumes the form of S. siliqua, but may be distinguished by the terminal bud not being elongated and tubiliform, and by being solid and not hollow inside. On one occasion I found what had evidently been a S. siliqua gall, occupied laterally by spongy matter containing 4 larvae undistinguishable from those of C. s. batatas, the elongated cell of the larva of C. s. siliqua being still in existence but contracted in diameter and empty. When these galls assume the elongate bunnion-like form, they are undistinguishable externally from the Tenthredinidous gall S. ovum, which occurs on S. cordata. and S. ovulum, which occurs on the same willow as S. batatas, but may be distinguished on cutting into them by the fibres being linear and radiating from the twig, whereas the other two galls are composed of a series of spongy lamellae at right angles to the axis of the twig, and moreover, when laid open to their base, ex-hibit the longitudinal slit made by the ovipositor of the mother Saw-fly. The smallest galls above referred to are only .15 inch in diameter; but there is a regular gradation from these to the larger and more conspicuous forms, and by isolating a number of the first in a separate breeding-jar, I ascertained that they produced the same Cecidomyia (7 specimens April 7 - May 10) and the same 3 parasites, viz. 2 Chaleidides and 1 Proctotrupide. When cut into about the last of July, the interior of this gall to the depth of .07 — .10 inch from the surface, is found to be white and fleshy; when cut into in the autumn or early in the spring, the substance of all but the very smallest, which are almost entirely woody and whitish, is found to be reddish-brown and of a dense, spongy texture, with indistinct fibres radiating from the twig. Some little distance from the external surface there are at this time a number of cells, about § of them tenanted by white, parasitic larvae, some hairy and some glabrous, be- longing to the Chalcididous genera Callimome and Decatoma (?), and about J of them tenanted by the orange-colored larvse of the Gall-gnat which originates the gall. In 3 or 4 instances I have seen the gall S. gnaphalioides growing sessile from the tip of (S. batatas. — Described from 100 — 150 specimens. Very com- mon near Eock Island on S. humilis. In galls similar to the last mentioned, small, elongate-oval galls, but growing on S. cordata. I found May 9 a larva undistinguish;ible from that of C. s. batatas and with the same breast-bone, but did not suc- ceed in breeding the perfect Grall-gnat. though I obtained many Chal- cidiffpe from these galls identical with two species bred copiously from S. batatas, one of which — a Decatoma ('^) with spotted wings — has hitherto occurred in no other gall, though a similar species infests Ci/- nips q. spongifica and other gall-flies. In November I found on *S'. discolor 8 galls, apparently identical both externally and internally with the iS. batatas found on S. humilis, 8 old and dry ones of the normal form which were all bored and strung along on the same twig, and 5 green and recent ones of the lateral, bunnion-like type on two diffbrent twigs. Their diameter was .19 — .40 inch. From the recent ones I obtained 6 larvae, which when compared with 6 taken from galls on S. humilis differed in no respect. In the preceding spring I had obtained 2 or 3 similar galls of the bunnion-like type from the same bush, from which I bred a large Microijaster, whence I infer that some lepidopterous larva had been living as an Inquiline in one of them, as the parasite was much too large to have lived in the body of C. s. batatas, and besides I have met with no instance of Ich- neumonidous insects being parasitic on Cecidomyia. I found at the same time several galls on the same bush, which, as has been stated to be sometimes the case in >S^. batatas, assumed the form of a slight, elongate-oval enlargement of the twig; but from these I bred nothing. < )n the whole, further investigation will be required to determine, whe- ther tbe imago produced from these galls on S. cordata and S. discolor is identical with Cec. s. batatas. It is rather singular, that in these »S. discolor galls I found no larvae at all of the Decatoma (?) and Calli- mome, which so greatly outnumber the larvae of C. s. batatas in the S. humilis galls. It is worth remarking, that the only two Cecidomyidous galls which appear to grow on more than one species of our Rock Island Willows — viz. aS'. batatas and C. siliqua — occur on as many as three species of them, and that these three species should in both eases be the samf", three, viz. S. humilis, S. cordata and S. discolor. The chances are very greatly against such an event happening, without some good and suffi- cient cause for it. Mr. Bebb informs me that there is a close alliance between S. humilis and S. discolor; but that neither S. cordata (=S. rigida) nor S. lucida is allied to the first two. While on this subject I may say that Mr. Bebb has re-examined the doubtful species of Wil- low referred to above (p. 546), and has concluded that it is certainly neither 8. nigra nor S. alba, and that it is not improbably S. fragilLs Lin., a species which has been introduced into N. A. from Europe.
