Decembeb 20, 1907] 



SCIENCE 



871 



e. g., 16 chromosomes in the first division in- 

 clude ten bivalents and sis univalents (two 

 idioohromosomes and four supernumeraries). 

 In the second division the supernumeraries 

 almost always unite with the idiochromosome- 

 bivalent to form a compound element; and the 

 facts indicate that the individual members of 

 this complex may undergo an asymmetrical 

 distribution to the spermatozoa, which probably 

 gives the explanation of the variations ob- 

 served in the somatic numbers of different in- 

 dividuals. The new proof given by the facts 

 of the genetic identity of the chromosomes, and 

 their possible bearing on certain phenomena 

 of heredity, were indicated. 



Variations in the Leaf Type of Liriodendron 

 Tulipifera during a Season's Growth: Dr. 



L. HUSSAKOF. 



The leaves were collected from a single tree 

 during three successive summers beginning 

 with 1904, and their variations in form statis- 

 tically studied. During 1905 and 1906 " aver- 

 age samples " (abont 500 leaves, representing 

 all parts of the tree) were collected at intervals 

 of about a month and systematically tabulated. 

 It was found that at the end of May the six- 

 pointed type of leaf constitutes over half the 

 total foliage (.58 in 1905; .65 in 1906), and 

 that the four-pointed type is totally absent. 

 During the next month there is a remarkable 

 growth of four-pointed leaves so that at the 

 end of June they constitute over 50 per cent, 

 of the total foliage. The six-pointed leaves be- 

 come reduced to about 35 per cent, of the 

 total. During the remainder of the summer 

 these figures vacillate only within about 5 per 

 cent. The leaves with 8, 10, 12 and 14 points 

 were also studied; each makes up only a small 

 per cent, of the total foliage, the last being 

 very rare. 



The tallc was illustrated by charts and 

 specimens. 



Orthogenesis in Gastropods : Professor A. W. 

 Geabau. (Illustrated with lantern slides.) 

 No abstract of this paper has been received. 



On October 14, 1907, the section met at 

 8 :15 P.M., in the American Museum of Natural 

 History. The evening was devoted to brief 



reports on summer work by members of the 

 section. Among others the following members 

 addressed the section : Professor W. M. 

 Wheeler : " A Study of Ants in Switzerland " ; 

 Professor N. L. Britton : " Recent Explora- 

 tions in Jamaica " ; Professor H. E. Cramp- 

 ton : " A Second Journey to the Society 

 Islands." 



Professor E. B. Wilson also gave a brief ac- 

 count of the summer work at Woods Holl, and 

 described some interesting experiments made 

 by him on the structure of living cells. 



Brief reports were also made by several other 

 members of the section, after which the meet- 

 ing adjourned. 



On November 11, 1907, after a short business 

 meeting, at which sectional officers for 1908 

 were elected, the following papers were read : 

 A Paleontological Trip to Northwestern Ne- 

 braska: Professor Henry F. Osborn. 

 Professor Osborn reported upon two excur- 

 sions, during the seasons of 1906 and 1907, 

 into the Lower Miocene beds of northwestern 

 Nebraska, variously known as Arikaree, Har- 

 rison and Rosebud. 



The recognition of these beds as containing 

 fauna transitional between the Oligocene and 

 Lower Miocene is due to the successive explora- 

 tions of Hatcher, Barbour, Peterson, Matthew 

 and Thomson. The lower division (Lower 

 Harrison, Lower Rosebud) is somewhat more 

 recent than the true Upper Oligocene of 

 Erance. The upper division (Upper Harrison, 

 Upper Rosebud) may also represent the be- 

 ginning of the Miocene, and is sharply defined 

 from the lower division by the absence of 

 certain mammals and the presence of others. 

 The formation as a whole is a very grand 

 one, extending continuously over 200 miles 

 east and west; varying in thickness from 

 1,200 feet in the west to 800 feet farther 

 east. It is, in fact, one of the most ex- 

 tensive, most readily distinguished, and most 

 definable of the Tertiary series, but it still 

 awaits accurate definition and distinction, 

 especially from overlying beds, partly owing 

 to the fact that it has been embraced under 

 the " Arikaree," which practically includes a 

 considerable part of the Miocene series. 



