igi4l CURRENT LITERATI 'RE 453 



In a study of Preissia commutata, Miss Graham 7 has emphasized the behavior 

 of the chromatin. In the vegetative cells of the gametophyte, the earliest 

 prophase is marked by an elongation of the nucleus and the appearance of 

 large chromatin masses on the linin strands. These strands thicken, forming 

 a spirem upon which the chromatin is borne in the form of chromomeres. The 

 spirem shows a temporary contraction, after which it segments to form 8 

 chromosomes. The disappearance of the nucleolus is sudden and coincident 

 with the appearance of the central spindle fibers, which suggests a material 

 relationship between these structures. At telophase the chromosomes elongate 

 to slender threads which lose their individuality in the reticulum of the 

 daughter nuclei. 



In the spore mother cell the reticulum gives rise to a leptonema spirem. 

 Many threads lie side by side, but whether this represents a parallel conjugation 

 or is without special meaning was not determined. Synizesis ensues. After 

 the knot loosens up, the spirem thickens and for a time the chromomeres 

 become more prominent. During a second contraction the spirem splits 

 longitudinally and soon segments to form the bivalent chromosomes. The 

 further behavior presents no unusual features. 



In both somatic and heterotypic prophases there are hyaline caps at the 

 poles of the nucleus, and in them, at least in the former case, the spindle fibers 

 are formed. Centrosomes or centrospheres were not found at any stage. — 



L. W. Sharp. 



Plant breeding in Sweden. — On account of the important practical results 

 obtained at the Svalof Institute, as well as because of contributions to the 

 science of heredity resulting from the extensive and exact investigations carried 

 on at this station, an authentic account of its history, ideals, and methods com- 

 ing from an authoritative source is especially welcome. The present director, 

 Nilsson, 8 sketches briefly the origin of the organization, emphasizing the 

 object, which was to arrive at absolutely practical results, and giving in some 

 detail the sources of its income. In the development of methods, attention is 

 directed to the comparatively small results coming from "selection in mass" 

 as practiced up to 1891, when "pedigree culture" was introduced. Thus the 

 method of isolating and studying pure lines derived from a single individual 

 was practiced at the Svalof station for ten years before it was advocated by 

 De Vries in his Die Mittationstheorie in 1901. With the adoption of this 

 radically new method, results have been more abundant. Xilssox emphasizes 

 the fact that the isolation of elementary species is only a preparatory auxiliary 

 for getting out properly the material to be utilized, the essential thing being 

 testing the practical value of the material and making the best selections. To 



7 Graham, Margaret, Studies in 

 Botany 27:661-681. pis. 54, 55. 1913. 



. 



Ann. 



8 Nilsson, H. Hjalmar, Plant breeding in Sweden. Jour. Hered. 5:281-296. 



1914. 



