256 



SCIENCE 



[N. S. Vol. XXXIX. No. 998 



eles similar to the tension zones between ecolog- 

 ical associations. By observation of these geo- 

 graphical tension zones it is possible to detect the 

 trend of geographical movements. The indica- 

 tions at Sugar Grove are that Boreal types are 

 giving way to others from the west and south. 

 (To be published in the Bulletin of the Torrey 

 Botanical Club, January, 1914.) 

 Variations in Iowa OaTcs: B. Shimek. 



Iowa occupies a peculiarly favorable position 

 for the study of variations in oaks. Here north- 

 ern, southern and eastern forms meet, and many of 

 them appear in groves bordering the prairies. 



Perhaps because of this, great variation is ex- 

 hibited by many plants, those of the oaks being 

 among the most striking and interesting. 



The paper deals especially with variations in 

 leaves and acorns, though other characters re- 

 ceive attention. Seventeen species and varieties 

 are reported from the state, but chief emphasis is 

 placed on variations in Quercus macrocarpa, Q. 

 alba, the Q. acuminata group, Q. rubra and the 

 Q. coocinea and Q. velutina group. The difficulty 

 in determining species is considered and the value 

 of specific characters is discussed, and special at- 

 tention is given to the discussion of such disputed 

 species as Quercus coccinea, Q. ellipsoidalis, Q. 

 boreale, Q. velutina, Q. texana and Q. Sehneckii. 



The distribution of some of the species is dis- 

 cussed, and the record of the range of distribu- 

 tion of several species is corrected. 

 Segregation of Characters in First Generation 



Hybrids from Stable Species of CEnothera: Geo. 



r. Atkinson. 



The parents are stable wild species of CEno- 

 thera (QJ. nutans Atkinson & Bartlett, and CE. 

 pycnocarpa Atkinson & Bartlett), i found growing 

 in the vicinity of Ithaca, N. Y. They have been 

 cultivated through two generations. They differ 

 in 25 to 30 clearly observable characters (a close 

 analysis will reveal more) distributed in rosettes, 

 stems, stem leaves, bracts, flowers, habit and prop- 

 agation. Beciprocal crosses give rise to hybrids 

 which show' segregation of characters in the first 

 generation. A number of the characters are con- 

 trast characters and behave as unit characters in 

 segregation into twin and tripled first-generation 

 hybrids. 

 Isomorphism in Capsella Hybrids: Henri Hus. 



In an earlier paper, presented at the Cleveland 

 meeting, the presence of a gene N, to which the 

 narrow character of the earlier leaves is due, was 



iSee Ehodora, 15: 83-85, 1913. 



demonstrated for Capsella Bursa pa.storis Setchelli. 

 This form was shown also to contain Shull 's gene 

 B, responsible for the deeply incised primary 

 lobes, as well as for the presence of secondary 

 lobes. At the time it was thought that in the F, 

 generation of a plant of the partial zygotic con- 

 stitution BbNn, the combination BN was not 

 formed (gametic repulsion). Experiments carried 

 on during 1913 have demonstrated that this com- 

 bination does exist and also that, whenever a plant 

 is homozygotic for N, the identical external ap- 

 pearance obtains, independent of whether the re- 

 mainder of the ascertained zygotic constitution is 

 BB, Bb or 66. Such combinations always yield 

 the form arachnoidea. 



On Physiological Isolation in Types of the Genus 

 Xanthium: Ghakles A. Shull. 

 Remarkable variations in the burs of what has 

 been considered Xanthium canadense Mill, have 

 been noticed in Kentucky, in Kansas and else- 

 where during the last several years. Three dis- 

 tinct types were selected in the fall of 1912 from 

 the local flora where all were growing together on 

 the same soil under identical conditions, for breed- 

 ing experiments. These types have bred true to 

 the parental generation, notwithstanding their 

 close proximity in the field and their unguarded 

 pollination. Differences were noticed in the burs, 

 seeds, leaves, pigmentation, etc.,. and in the length 

 of time required for the development of the repro- 

 ductive organs. Because they bloom at different 

 ages the types tend to remain distinct, although 

 there is evidence that occasional hybrids may oc- 

 cur under natural conditions. The genus needs 

 revision based upon experimental investigation. 

 On an Abnormality in the Floxoer of the Bellwort 

 {Oakesia sessilifolia) which Prevents Seed For- 

 mation: A. F. Blakeslee and A. F. Schtjlze. 

 The abnormality consists in transformation of 

 stigmas into anthers containing pollen grains 

 which in sugar solutions germinate, as well as 

 pollen from the normal stamens of the flower. 

 Such abnormal flowers do not set seed. 

 Variability in a Vegetatively Pure Line of a Her- 

 maphroditic Mucor: A. F. Blakeslee. 

 Separation cultures from a single spore sowing 

 of the mucor tested gave a small percentage of 

 colonies sharply different from the stock form. 

 The variations consisted in absence and increase 

 or decrease of zygospore production, peculiarities 

 in color, density and rapidity of mycelial growth, 

 differences in height of mycelial fllaments, the 

 almost exclusive production of yeast-like cells in 



