igi 2 ] CURRENT LITERATURE 549 



sperms, possessing a siphonostele with strong development of secondary wood, 

 had uniseriate or linear rays, such as characterize the conifers. During the 

 warmer climate of the Mesozoic, " sheets of storage tissue were built up from 

 congeries of uniseriate rays about the persistent leaf traces of evergreen 

 angiosperms. This primitive type of foliar ray has persisted in certain 

 species of primitive families (Casuarinaceae, Fagales, etc.). Later changes in 

 'climate modified the storage conditions, and in the majority of living dicoty- 

 ledons the aggregated units of foliar ray tissue have been diffused through 

 the stem, and in general the evidence of their former relation to leaf traces has 

 disappeared. In a small number of forms the primitive aggregate type has 

 been " progressively compounded or solidified, ,, and* the result is the con- 

 pound or multiseriate ray (deciduous oaks, etc.). In many families there 

 has been a reversion to the primitive uniseriate condition. As a consequence, 

 in the modern species the foliar ray of the primitive aggregate type has been or 

 is being reduced, diffused, or compounded. The evidences of reduction are 

 interesting and important in any scheme of classification. For example, 

 Castanea and Castanopsis are reduced members of the oak family, and Alnus 

 mollis and A. acuminata are reduced species of Alnus. 



It is increasingly evident that the woody cylinder of angiosperms is very- 

 far from being a structure of phylogenetic simplicity. — J. M. C. 



Bog vegetation. — In studying the various problems connected with the 

 peat bogs of Ohio, Dachnowski 18 has made a careful enumeration of the various 

 plant associations involved, and traced the variously modified successions' 

 which occur. Fortunately he has not been content with observations, but 

 has attempted various lines of quantitative study of the factors involved, such 

 as the height and variation of the water table, the acidity of the soil, and the 

 evaporating power of the air. He has also begun a series of chemical analyses 

 of bog water and peat soils. The preliminary results 19 are valuable as being 

 suggestive of lines for future investigation rather than as affording solutions 

 for any existing problems. The chemical changes which take place in the 

 transformation of vegetable matter into peat are only imperfectly understood, 

 but as they are observed as exhibited in passing from the imperfectly formed 

 fibrous material to the competely transformed structureless peat there is a 

 relative loss of oxygen and hydrogen and an increase of carbon and nitrogen 

 simultaneously with an increase in the reducing processes in the soils. The 

 complexity of the problem of relating the vegetation to the chemical nature 

 of the substratum is indicated, as well as the possible importance of the decom- 

 position products of proteids and carbohydrates that are now beginning to be 

 isolated and identified. — Geo. D. Fuller. 



18 Dachnowski, A., The succession of vegetation in Ohio lakes and peat deposits. 

 Plant World 15:25-39. 1912. 



19 , The relation of Ohio bog vegetation to the chemical nature of peat soils. 



Bull. Torr. Bot. Club 39:53-62. 191 2. 



