192 



SCIENCE 



[N. S. Vol. XXXIII. No. 840 



Sex Latency in the GametopJiyte of Onoclea 

 strut hiopteris: F. C. Newcombe. University 

 of Michigan. 



Tlie experimental work of Miss Wuist on the 

 sex of tlie gametophyte of Onociea struthiopteris 

 sliowed, as published last year in the Botanical 

 Gazette, that the female gametophyte may be 

 made to give rise to antheridia. Miss Wuist's 

 later work has shown that spores of the same 

 species, which formed at first narrow ameristie 

 plants bearing antheridia, subsequently developed 

 heart-shaped proliferations at their apices bear- 

 ing arehegonia. To stimulate the outgrowth of 

 the archegonia-bearing proliferations, the anthe- 

 ridia-bearing gametopliytes were transferred from 

 humus soil in pots to a Knop's solution, where 

 they produced the meristic, heart-shaped, sec- 

 ondary gametophytes with their arehegonia. 

 Reversible Sex-mutants in Lychnis dioica: Geobge 

 Habkison Shull, Station for Experimental 

 Evolution, Carnegie Institution. 

 Hermaphrodite mutants were discovered in 1908 

 in cultures of Lychnis dioica, and the following 

 year a report was made on the first generation 

 cross of these with females and normal males. 

 The present paper presents data from more than 

 one hundred families in which these hermaphro- 

 dites were used, most of these families represent- 

 ing the second generation from the original her- 

 maphrodites. It is shown that the hermaphrodite 

 character is a modified male condition, not due 

 to the presence of an independent modifying fac- 

 tor which was suggested by Correns, but obviously 

 a modified condition of the male-producing gene 

 itself. The hermaphrodite character is not trans- 

 mitted by the egg, but only by the sperm. Among 

 the offspring of these hermaphrodites have ap- 

 peared a few normal males in such small propor- 

 tions (a small fraction of one per cent.) that they 

 can only be considered male mutants, since they 

 also breed true to their male character. The 

 appearance of hermaphrodite mutants in families 

 produced from normal males and the appearance, 

 in turn, of male mutants in families produced by 

 hermaphrodites, suggest reversible modifications 

 of a single gene rather than the addition of a gene 

 to those previously present, and a subtraction of a 

 gene from them. These results may thus have an 

 important bearing upon the " presence and ab- 

 sence " hypothesis. 



An Isolated Prairie Grove and its Ecological 

 Significance: Henby Aixan Gleason, Univer- 

 sity of Michigan. 

 Bur Oak Grove is located in Champaign County, 



HI., and is about one by three miles in size. It is 

 peculiar in being located at some distance from a 

 stream and surrounded on all sides by prairie, 

 while most of the forest tracts in central Illinois 

 are along the larger water courses. The prevail- 

 ing trees in the grove are Quercus velutina, Q. 

 imbricaria, Q. macrocarpa, Carya ovata, G. cordi- 

 formis and Juglans nigra, with scattered indi- 

 viduals of other species. The variation in the 

 composition of the forest indicates that it mi- 

 grated into the region from the northeast. The 

 grove is not continuous, but is broken by areas 

 of low ground which contain permanent standing 

 water. On the moraine north of the grove are 

 found some plants which are regarded as forest 

 relies, now growing in the prairie. It is concluded 

 that the whole moraine was formerly covered with 

 forest, which extended also some distance out on 

 either side. Since the introduction of prairie iires 

 this forest has been destroyed, except Bur Oak 

 Grove, which is protected by the standing water 

 against attacks of fire. The more general con- 

 clusion drawn is that forests were formerly of 

 much wider extent in Illinois than at present, but 

 it is distinctly stated that the prairies do not owe 

 their origin to prairie fires. 



Evaporation in its Relation to the Prairie Prob- 

 lem: B. Shimek, Iowa State University. 

 The fact that surfaces exposed to the south and 

 southwest in the Mississippi Valley are treeless 

 has been frequently noted. Where changes in 

 topography are abrupt the transition from forest 

 to prairie is likewise abrupt. The prairie plants 

 are essentially xerophytic, the forest plants meso- 

 phytic. The former are found upon the siirfaces 

 exposed to sun and summer winds, the latter in 

 sheltered places. Field observations on rate of 

 evaporation on treeless and forested areas, made 

 in western and northwestern Iowa, show that it 

 is much greater on prairie surfaces than in the 

 adjacent forest, and materially greater than on 

 contiguous areas which had been covered with 

 forest but are now cleared. This is true even in 

 the vicinity of larger bodies of water. The results 

 of these observations are presented in tabulated 

 form, and are represented by curves. They show 

 that evaporation increases with temperature and 

 velocity of the wind, and that when the tempera- 

 ture is- high the fluctuations in evaporation are 

 caused by changes in wind velocity. The bearing 

 of these results upon the prairie problem is dis- 

 cussed. 



Structure of Adult Gycad Trunks: Chables J. 

 Chambeblain, University of Chicago. 

 While the structure of the cycad seedling is 



