336 



SCIENCE. 



[Vol. II., No. 31. 



In the discussion of the paper, Prof. E. D. Cope 

 inquired as to tlie likelihood of a reversion to a 

 variety of non-spurred orcliids, an idea which met 

 with a favorable response from the author. 



Origin of the flora of the central Ne\7-York 

 lake region. 



BY yf. K. DUDLEY OF ITHACA, N.Y. 



The region referred to contains a seiies of lakes, 

 and is bounded on the west by the Genesee river 

 and on the east by Oueida lake. It is of a low, sandy 

 character, the shores of the lakes having but a slight 

 elevation; but towards the north the country gradii- 

 ally rises to a level of 2,000 feet above the sea. The 

 whole region may be regarded as a series of old 

 eroded valleys, filled with drift deposits, and having 

 occasional lake-basins; its entire characteristics being 

 such as would naturally give rise to a peculiar flora. 



Professor Dudley described seven species among 

 a large and varied flora peculiarly localized in this 

 lake-country, the natural or ordinary habitat of 

 which is variously situated to the south-west, west, 

 and north-west. The conclusion he sought to estab- 

 lish was that tlie wateis of the great lakes liad 

 formerly flowed through these valleys, and carried 

 with them these several varieties of a widely scat- 

 tered flora. 



The remarks which followed the reading of the 

 essay favored this theory, and pointed especially to 

 the abrupt eastern limit of the species in question. 



Development of a dandelion H.o'wer. 



BY J. M. COULTER OF CRAWFORDSVILLE, IND. 



Bt means of crayon illustrations, the author of 

 this paper displayed the changes which the different 

 parts of a dandelion-flower undergo in the process of 

 growth to full maturity. The main object was to 

 demonstrate the place, and metiiod of origin, of the 

 ovule. 



{ZOOLOGICAL PAPERS.) 



Mya arenaria: its changes in pliocene and 

 prehistoric times. 



BY E. S. MORSE OF SALEM, MASS. 



At a previous meeting of the association, the au- 

 thor showed that the species of shells found in the 

 Indian shell-heaps along the coast of New England 

 differed in their proportionate diameters from the 

 same species living to-day. He pointed out, more- 

 over, that species belonging to similar genera, in the 

 shell-heaps of Japan, had clianged in precisely simi- 

 lar ways. It was important to find out, if possible, 

 the' cause of these changes. A comparison between 

 the shells of two common species, found north and 

 south of Cape Cod, gave indications that temperature 

 was the inducing cause. The two species selected 

 were Mya arenaria and Venus mercenaria; the for- 

 mer extremely variable, the latter very constant, 

 in its characters. Specimens of these species had 

 been collected in great numbers, both recent and an- 



cient. The following are the indices, of Mya are- 

 naria: — 



RECENT. ANCIENT. 



South of North of 



Cape Cod, Capu Cod, 



61.42. 61.67. 



of Venus mercenaria: — 



Soulli of North of 



Cape Cod, Cape Cod, 



81.01. 81.10. 



South of 

 Cape Cod, 



North of 

 Cape Cod, 



South of' North of 



Cape Cod, Cape (,'od, 



81.61. 81.81. 



Since the waters south of Cape Cod are much 

 warmer than those north of Cape Cod, it was reason- 

 able to suppose that these changes were due to tem- 

 perature, and that the liigher inde.x of the ancient 

 specimens found in the Indian deposits might indi- 

 cate a colder climate. This supposition receives some 

 support in the fact that a measurement of specimens 

 fotind in the gl.acial clays about Portland, Me., and 

 on the Kennebec river in the same state, gave tlie high 

 index of 60, and a number of Norwieli and Red Crag 

 fossils of Mya, which he had the opportunity of meas- 

 uring at the British museum, had an index of 64; 

 recent Mya from South End, Eng., having the low 

 index of 58.30. 



It was interesting to observe, that measurements of 

 Mya/ in Japan gave, for the southern form, an index 

 of 61.10, and, of a more northern form, 62.50. 



Ill the discussion which followed, Mr. Morse stated 

 that he had made similar observations with regard to 

 other shell-fish. 



Some recent discoveries in reference to Phyl- 

 loxera. 



BY C. V. KILEY OF WASHINGTON, D.C. 



Every new fact in the life-history of the insects of 

 this genus has an exceptional interest, beoause of its 

 bearing on the destructive grape-vine Phylloxera. 

 The genus is most largely represented in this country 

 by a number of gall-making species on our different 

 hickories, and the full annual life-cycle of none of 

 them has liitherto been ti'aced. The galls arc pro- 

 duced, for the most part, in early spring; the winged 

 females issue therefrom in early summer; and thence- 

 forth, for the remainder of the year, the where- 

 abouts of the insect lias been a mystery. The author 

 has for several years endeavored to solve this mystery 

 and at last the stem-mother (the founder of the gall), 

 the winged agamic females (issue of the stem-moth- 

 er), the eggs (of two sizes) from these winged fe- 

 males, the sexed individuals from these eggs, and the 

 single impregnated egg from the true female, have 

 been traced in several species. There is some evi- 

 dence, though not yet absolutely conclusive, that this 

 impregnated egg hatches exceptionally the same sea- 

 son; also, of a summer root-inhabiting life. In Phyl- 

 loxera spinosa, wliich forms a large roseate somewhat 

 spinose gall on Carya alba, and which has been most; 

 closely studied, the impregnated egg is laid in all 

 sorts of crevices upon the twigs and bark and in the 

 old galls, in which last case they fall to the ground. 



