270 



SCIENCE 



[N. S. Vol. XXV. No. 633 



gote condition, which may determine the 

 failure or success of the plant in' establish- 

 ing itself in a given habitat. In the case 

 of competition between a mutant and its 

 parent form, the chances of persistence of 

 the former may be increased or decreased 

 through hybridization, according as they 

 Mendelize or produce constant hybrids. 



Species which hybridize readily afford a 

 method for the quantitative study of cross 

 pollination. 



The Morphology of Lemna trisulca: Otis 



W. Caldwell, State Normal School, 



Charleston, 111. 



The sporophyte body is regarded as com- 

 posed of stem, root and leaf, not as an ' un- 

 differentiated shoot.' Floral structures, 

 by their relative position and age indicate 

 that there is instead of a single flower an 

 inflorescence consisting of one carpellate 

 and two staminate flowers all borne on a 

 greatly reduced spadix. Carpellate and 

 ovular structures indicate relationship 

 with the more complex Aracese. 



The tapetal cells may grow into the 

 loculus, become multinucleate and almost 

 join cells from the opposite side. Spore 

 mother cells may act in the same way. 

 Spore mother cells and spores may dis- 

 organize at any time. 



No case of indirect division in the germi- 

 nation of the microspore was found, the 

 divisions observed being amitotic. 



The female gametophyte rarely matures, 

 the ovular structures disorganizing at any 

 time. Vegetative reproduction is depended 

 upon almost exclusively. Seed production 

 is seldom attempted and almost completely 

 unsuccessful. 



The Structure and Wound-Behavior of the 

 Cedar of Lebanon: Edward C. Jeffrey, 

 Harvard University. 



The Abietineee are divisible on anatom- 

 ical and reproductive characters into two 

 distinct subgroups, the Pinese and the 



Abietese. The former are characterized by 

 deciduous cones with non-deciduous scales, 

 by the resin canals of their secondary 

 wood, and by the peripheral resin canals 

 of the primary xylem of the root. The 

 latter by non-deciduous cone axes with 

 deciduous scales, by the absence of resin 

 canals in the secondary wood and by the 

 median resin canal of the primary xylem 

 of the root. The cedar is distinguished 

 among the Abietese by the fact that it 

 forms, as a result of injury, resin canals in 

 the secondary wood both in the vertical 

 and in the horizontal planes, which are con- 

 tinuous with the resin canals outside the 

 woody cylinder. Further in the primary 

 wood of the root, although the median 

 single resin canal, which is characteristic 

 for the Abieteffi, is present it is often ac- 

 companied by apparently vestigial periph- 

 eral marginal canals, similar to those 

 found in the Pinese. These facts together 

 with the great geological age of Cedriis 

 (older than any others of the Abietese) 

 tend to show that it is the most primitive 

 of the Abietese and has come from the same 

 parental stock as the Pinese. 

 Tyloses in the Tracheids of Conifers: 

 MiNTiN A. Chrysler, Harvard Univer- 

 sity. 



Tyloses have been regarded as normally 

 absent in the tracheids of conifers. An 

 examination of the heart wood of the root 

 shows that in various species of Pinus true 

 tyloses occur. These are in the form of 

 vesicular outgrowths from adjacent medul- 

 lary ray cells, and are found in all stages 

 of projection into the tracheids. They 

 are quite distinct from the tyloses which 

 have long been known to be present in the 

 resin ducts, and among the conifers seem 

 to be confined to the genus Pinus, where 

 they occur in all the species yet examined. 

 The Homologies of the Medulla in the 

 Filicales: J. Horace Faull, University 

 of Toronto. 



