52 SUMMARY OF CURRENT RESEARCHES RELATING TO 



paper made a numlser of crosses between types of maize previously 

 selfed from three to six generations, with the result that the crossed 

 seeds showed an increase in weight ranging from 5 to 35 p.c. The 

 greatest increase was obtained where the proportion of selfed to crossed 

 seeds was greatest, suggesting that the heterotic seeds grew at the 

 expense of the selfed seeds. There appears, however, to be no real 

 correlation between the amount of increase in weight and the proportion 

 of two kinds of seeds. The writer finds no confirmation of Nemec's. 

 theory that endosperm hybridization is " an adaptation resulting in an 

 alteration of the food-supply to accord with the properties of a hybrid 

 embryo," and doubts whether heterosis " can be entirely removed from 

 the category of results due to indefinite physiological stimulations." 



S. Gr. 



Structure and Development. 

 Vegetative. 



Ray-System of Quercus. — L. M. Langdon {Bot. Gaz., 1918, 65, 

 318-23, 22 figs.) has studied the ray-system of Q. alha in order to 

 determine the effects resulting from certain conditions, e.g. age of tree, 

 vigorous or retarded growth, etc. Observations show that neither age 

 nor position of the shoot has much effect upon the ray-formation, bub 

 that during decreasing vigour of growth of the mature wood, the 

 " multiseriate rays appear at progressively later stages in the develop- 

 ment of the stem." Multiseriate rays are found in seedlings and in the 

 first annual ring in the vicinity of lateral leaf-traces. The peculiar 

 formation of the wood and cambium is due to the influence of outgoing 

 leaf-traces upon the general structure of the xylem cylinder. S. G. 



General. 



Statistical Investigations on Plant Formations. — C. Raunkiaer 

 {Kgl. Danske Videnskah. Selskah. Biol. Meddel., 1918, 1, pt. 3) contributes 

 a paper (written in French) of considerable detail, dealing more 

 especially with northern Europe. A general description is given of 

 (1) the frequency and distribution of the species entering into the forma- 

 tions ; (2) the relative proportions of the species ; and (3) the common 

 biologic characteristics by which the species of a formation adapt 

 themselves to their habitat. The writer then summarizes the chief 

 points to be noted for a complete ecological description of any given 

 area, which are briefly as follows : — The term " formation " is used tO' 

 describe the vegetation of any area which is perceptibly homogeneous as 

 to chief species. Where the natural conditions have not been interfered 

 with, the vegetation attains a sort of equilibrium, each species being 

 confined to that part of the habitat to which it is best suited. No two 

 species are ever quite similar in their methods of adaptation, so that a 

 difference in floristic composition corresponds to a difference of con- 

 ditions. A most important feature of plant formations is the frequency 

 with which the different species occur ; this is usually estimated as. 

 a percentage of the number of specimens collected in a given area. 

 Another important feature is the degree of prosperity of the different 



